While the Heroes are normally created to protect the divine tree the Shinju, what if a Hero was made for the opposite side? What if the rebelling gods made their own Hero. This was the beginning of Yuna Akamine, a mysterious "hero" of the past summoned into the present by the rebelling gods in the video game "Yuki Yuna is a Hero: A Sparkling Flower."
Yuna Akamine hails from a chaotic period after the first generation of humans when chaotic infighting among humans was normal. She was given very limited divine powers by the Shinju not for fighting the vertex... but for fighting other humans, for forcing order upon their internal world as chaos was deadly in the time of the vertex. This was a time when some humans still revered the heavenly gods and thought their vertexes were their divine manifestation, a time when humans were unsure of the rightness of either side. This was the confusing time Yuna Akamine hailed from.
Eventually, she was brought back in the time-bending adventure of the game she features in. Finding out the tragic fates of the other Heroes, the deaths and sufferings they had to go through, she strived to keep them trapped in the Shinju's dimension to save them. Eventually, Yuna Takashima and Yuna Yuki help sway Yuna Akamine from her dark path serving the rebelling gods and to trust the generations of Heroes to save the world.
Yuna Akamine was able to at least somewhat physically contend with Yuna Takashima. The First generation would regularly fight hundreds of unevolved Vertexes, Stardust who are said to be immune to any of the weapons of humanity and created great natural disasters requiring power in the megaton range. These Stardust underwent hyper-evolution into perfect vertex which the First Generation Heroes could fight with extreme difficulty. with Wakaba Nogi bisecting a Serpentine Vertex made of hundreds of stardust.
In terms of speed, Yuna Akamine can keep up with the first generation of Heroes who themselves can outpace the stardust and vertexes who are said to outpace any human weapon including hypothetically missiles traveling at hypersonic speeds. Beyond that, she may scale in reaction speed at least partially to the likes of Gin Minowa who has three seperate feats of blocking light with the Heroes also able to react to the vines of the Shinju which traveled into space in seconds, calced at roughly 3%c
Yuna Akamine also has a Mankai form which, while she's unlikely to use most of the time, can bolster her stats massively and should make her relative to Yuna Takashima's Shuten-Douji, an attack that is explictly stated to have 50 teratons of energy, which is enough energy to destroy a country. Mankai Heroes can also move fast enough to quickly travel in space at massively hypersonic speeds.
Yuna has the powers of the other Heroes. As one who is both soul and body, her regeneration and endurance are amplified as well as all of her physical stats. She can superleap hundreds of meters, has an enhanced awareness, and an immunity to time stop. Most notably, she has a fairy which grants her immortality. And when they say immortality, they really mean it with even universal-level deities being unable to kill a hero, as the fairies are a part of the gods. A hero who wanted to kill herself literally couldn't because the fairy forcibly keeps them alive no matter what.
Yuna also has unique powers given by the evil gods. The evil gods granted her the power to control the vertex to act as their general. Beyond that, she has psychic powers. She can read the minds of others and cause them to relive memories. Both her and her fairy can disguise themselves as other people. Her fairy can enter into the minds of other people and ask them questions about themselves. If they can't answer, the fairy possesses them. The fairy usually asks personal questions Akamine has surmised are difficult for them to answer honestly. It required a heart that was honest to itself like Yun aTakashima or Yuna Yuki to defeat this trick of the fairy. Beyond this Yuna Akamine can summon gusts of wind to teleport her, can perform almost literally substitution jutsu (with Akamine's family being compared to spies and ninjas), and perhaps most strongly has the ability to BFR her opponents within her mind so they can't escape. The irony is Yuna Akamine, the girl who found it hard to communicate with others, who lived in a world of confusion and mistrust, gained the ability to communicate directly with the hearts of others.
While Yuna Akamine is far from the best fighter of the Heroes, she is quite possibly the most intelligent, having manipulated all the others after they were summoned from the time, leading them along her grand mastermind plot. Her family, the Akamine family, are also a family of highly trained spies and ninjas with her having even outside her powers, significant skill in stealth.
In terms of weaknesses, Akamine has the same physical weaknesses as the other Heroes. Mankai can cripple her, and her fairies can't protect her from non-physical forms of attack. Compared to the other Heroes, Yuna Akamine is actually relatively physically weak, only having attained limited divine powers to fight other humans rather than the swarms of Vertexes.
Mentally she has more notable weaknesses. Yuna was never trying even somewhat hard against the Heroes, leaving them clues as to her plot, wanting to fight and enjoy fighting rather than focusing on winning, treating her enemies with a strange amount of politeness rather than using deceptive pragmatic fighting like her powers would suggest. Granted this may not apply in most situations as Yuna Akamine's true goal it was revealed was she had seen the fates of the other Heroes and wanted to keep them trapped inside the Shinju forever so they would never have to suffer death and heartbeat. So against most characters, this may not apply. Also, she has real trouble communicating with people.
Name: Yuna Akamine
Origin: Yuna Yuna is a Hero
Powers and Abilities: Enhanced Physical Stats, Regeneration, Leaping, and Senses, Physical Immortality, can control the Vertexes, Mind-Reading, Memory Manipulation, Shapeshifting, Possession, Teleportation, Wind Manipulation, Ninja Skills, Mental Plane BFR. Resistance to Time Stop
Weaknesses: Fairy can't protect against non-physical attacks, Mankai damages her body severely, can't possess people who are completely honest with themselves, can't communicate well
Destructive Capacity: City Level, Country Level with Mankai
Range: Likely hundreds of kilometers
Speed: Hypersonic, Massively Hypersonic with Mankai, Likely Relativistic Reactions
Durability: At least star level (Fairy barriers can withstand things like a black hole), potentially universe level (is a part of the universe level gods which even the other gods can't easily kill)
Stamina: Presumably higher than normal (Heroes have enhanced endurance)
Standard Armor: Hero Transformation Device
Intelligence: At least gifted, manipulated all the other Heroes, evading capture by them for a long time, comes from a line of spies and ninjas
So how would the dark Hero do in other verses?
In Marvel Comics, Yuna would be roughly a Mid Metahuman Tier fighter, comparable to other feats like Iron Fist defeating an opponent whose power was measured in the hundreds of megatons or Electro creating large electric storms. She'd be slower than almost everyone as most characters in this tier scale to lightning timing or higher, but her reaction speed is high enough that it shouldn't be a big problem.
Ironically, her unique powers are kind of meh for this tier in Marvel and it's her general hero abilities that would be much more notable. Her psychic powers are very low level for Marvel and almost any notable hero can probably just resist her powers, outside maybe her mental BFR. Similarly, her intelligence and ninja skills while impressive for her universe are pretty much bog standard for the Marvel Universe with almost every hero having impressive intelligence feats, ninja-like training in stealth and feats or training in seeing-through deception. Against characters like Spider-Man, Wolverine, or the Fantastic Four the only one of her unique powers that would be really notable is her mental BFR whcih would be a fairly unique one-shot type of attack.
What's more relevant is her general powers as a hero, in particular her fairy immortality. This would be an extremely broken type of defense on the same tier as something like Captain America's shield or Wolverine's claws. This would definitely give her a niche as a defensive type character who can fight most characters in the tier, though whether Wolverine's claws could get through Fairy Immortality would be interesting to see. Overall she'd be in the same range as most Marvel Metas with the most interesting things about her being her special BFR technique, being technically able to briefly shoot up to High Meta status, technically, and basically having a vibrainium suit at all time.
In DC Comics, Yuna Akamine would be roughly a Beta Metahuman similar in tier to characters like Hawkman, Fire, and Ice, with her Mankai form being closer to the level of a Royal Atlantean.
In the DCU, Yuna Akamine's power would be a lot more dangerous with most Beta Metahumans being unable to keep up with her power level, especially with her ability to use Mankai, and her psychic powers may get some use with less of the tier having resistance to mental shenanigans. On the other hand, the DCU even at a relatively low tier of power has more ways around Akamine's immortality with characters like Batman having various mentally affecting gadgets and techniques including engaging in a mental plane battlefield, Harley Quinn and the Joker having mild metafictional abilities, John Constantine having just... a hundred different things he can do etc. While Yuna Akamine would be a lot more overpowering against characters without a way around her fairy immotality, it would be a higher risk scenario for her as well.
In the Puella Magi-verse, Yuna Akamine would be a real trouble to add to the verse as she would do really well against Puella Magi but really poorly against witches, meaning she would only be able to hurt the heroes. She's roughly in the same power range as Homura thought a witch could maintain a barrier encompassing an entire copy of Mitakihara Town and the surrounding area, though Mankai can temporarily amp her to the level of someone like Isabeau who could create a barrier across all of France.
All the standard abilities of the Puella Magi are physical based abilities that wouldn't get past a Fairy's barrier. There are almost no Puella Magi normally with abilities that would be good against someone with the Hero System with many of the Magical Girls not being fully honest with themselves and likeable to Yuna Akamine's form of possession. Even Homura would struggle to get past Yuna Akamine given Yuna has time stop resistance. On the other hand, all Witches have as standard lots of non-physical powers like lifeforce draining and mentally manipulating people into suicidal homicidal insanity which would bypass fairy immortality entirely.
There are a few Magical Girls that could take her down. In the Tart Era for instance even outside Holy Tart herself, Riz has the Gates of Hell technique which with a self-sacrifice could bfr Yuna Akamine potentially and in Oriko Magica Kirika had the power to change her own form even giving herself the powers of a witch to protect Oriko, with witch powers being able to take down Yuna. However she'd be a big threat until she was taken down by a high tier magical girl like these.
In the Nanoha-universe, Yuna Akamine would likely rank as an upper B rank mage in terms of raw power being above overall B Rank Arf who could create a storm with her raw power but below A Rank Chrono who could freeze a sea, calced in the teraton range. However Yuna could temporarily rise into A Rank with her Mankai.
As might be expected, Yuna's fairy immortality would be difficult for most of the wizards of the Nanoha-verse to fight as their magic tends to lack the ability to hit non-physical aspects of their enemy with the most likely weapons of most TSAB Mages to work against Akamine being binding spells or dimensionally trapping her. On the other hand, whether Yuna's attacks would work on them depend a lot on whether the powers Yuna was given by the evil gods qualify as "magic" or not. Personally I'm of the opinion it would, in which case the MGLN-verse Mages barrier against magic should protect them. This is not an impenetrable defense however as it's a pretty normal forcefield proportional to their attack potency meaning assuming Yuna can reach their level of power, she can break the barrier and then use her magic on them directly (or just punch them as their forcefield is where their durability comes from.)
Overall, Yuna would likely be a relatively even match for an A Rank Mage like one of the Wolkenritter as it would be a battle of them to trying to find a way to trap an immortal enemy before she goes mankai and breaks through their defenses. That said she would be no match for one of the Aces (Nanoha, Fate, or Hayate)
In Skullgirls, Yuna Akamine would fit in pretty normally stat wise. Her level of power is consistent with most fighters in the verse scaling from Double maintaining a large dimension within her as well as Hungern being stated to consume half of New Meridian in a quick timeframe and the Skullgirl Marie throwing a tower across the city, calced into the megaton range, alongside numerous hypersonic feats. With her Mankai she would reach a higher tier in the verse, being comparable to the Skullgirl Nancy who withstood a blast from Eoberung that annihilated dozens of smaller countries and spread her aura across an entire country-spanning battlefield giving Queen Nancy and Eliza very similar stats to Mankai Yuna Akamine.
How Yuna would do against the cast varies heavily. Someone like Valentine would see Yuna Akamine as a nightmare to fight being someone who can exploit her psychological contradiction, is immune to all her attacks and poisons and even her time stopping, and can one-shot her. On the other hand someone like Peacock would be a nightmare for Yuna having metafictional toon powers that allow her to casually teleport back from mental bfr via fourth wall shenanigans, easily bypass physical immunity with metafictional interaction or a violence ball or a soul-deleting theonite cannon, things which Yuna's fairy would have no way of protecting from, can obviously see through any of her deceptions and has no real psychological complications within being completely honest with herself. Someone like Beowulf would be somewhere in the middle with most of Beowulf's tactics being unable to hurt Yuna Akamine conventionally and could be deceived by her trickery, but has metafictional attacks and teleportation to bypass mental bfr and fairy immortality, and which Yuna Akamine's form of possession may or may not work depending on your interpretation of his character.
Overall Yuna Akamine would be a fairly balanced addition to the verse having a very powerful couple of abilities but weak to the myriad forms of metaphysical forms of attack in the verse, especially to manifestations of Theonite's destruction. Nonetheless, without information, she could definitely be a valuable asset against a Skullgirl helping to tank a few blows before she finds out Akamine's weakness.