Blade, an anemo destruction unit, is an upgrade from hu tao. He is afflicted with mara and is part of the stellaron hunters alongside Silver Wolf and Kafka.
Blade overthrew Dan Heng as HSR's wind dps.
Blade's skill sacrifices hp to buff his NA and dmg bonus. His NA does blasts, giving him some aoe, unlike hu tao who is more single target (hunt). While in this buffed mode (hellscape), his NA do not create skill points. His NA will also consume more of his hp. His ultimate does a blast of aoe anemo damage to enemies while setting his hp to 50% (this can drain or heal hp). So far this appears derivative of hu tao's kit and maybe even similar to Xiao with the hp drain over time (when using NA).
However, this is where Blade becomes better than hu tao: Each time Blade takes damage (or loses hp from skill), he gains 1 stack of charge. Once he reaches 5 stacks of charge, he will do an aoe attack on all enemies on field, while restoring his hp. Hu tao lacks this kind of charge mechanic. So the burst setting his hp to 50% can have one of the following effects: if under 50% it heals him, if over 50% it gives him 1 stack, and if at 50% no additional effect.
Moreover, Blade's burst deals additional damage based on how much hp he has lost so far in battle (tally capped at 90% his max hp). Using his burst will reset this value to 0, and hp lost will start accumulating again. He can also heal himself when attacking weakness-broken enemies.
His attacks scale directly with hp and atk (dual scaling like Dehya), whereas hu tao deals atk-scaling damage, and hu tao's skill buffs her atk based on her hp. And hu tao has a cd for her skill use, whereas Blade does not (it is just that his NA do not create sp).
While Blade could benefit from a shielder to avoid falling in battle, he will not gain a charge if attacked when shielded (and thus may not accumulate charges as fast). He needs to take damage from the enemy, so this is another example where a shielder can result in a dps loss.
So Blade synergizes better with abundance units (like Natasha) than preservation units (like March or Gepard). Having a healer is almost a must for Blade (although he can solo some content). Other than that, the usual suspects for supports can be teamed with him: Silver Wolf, Bronya, etc.
Also since Blade is SP-neutral, he can also be paired with other dps units like Jing Yuan or others without the team devouring all the SP.
Blade is a classic example of a destruction-type character: he possesses great survivability, can self-heal, can tank a lot of hits, and once he tanks enough hits he will unleash more damage. And the more hp he loses, the more damage he does (this is amplified further by his E4). So he has this sacrificing mechanism: he can sacrifice some of his own health but in return do more damage to the enemy. And because Blade scales with hp and can heal himself, he tends to have greater survivability in battle so he can afford to sacrifice some hp.
As stated in his 'keeping up with star rail' video, power comes with a price, but that price can become power. This is the path of destruction: converting your sacrifice into increased damage.
When he gets healed, Blade says there is 'no need', whereas other characters like Jing Yuan or Himeko would say 'thank you'. This aligns with how Blade, as a destruction character, has built-in survivability and self-healing abilities. Moreover, what he says is almost true in some situations as Blade's burst sets his hp to 50% and heals himself, sometimes making more healing unnecessary or redundant. (In practice, Blade actually does benefit from a healer, but it is possible for him to solo some fights without any healer.)
The imagery of how he cuts himself with his sword to draw blood is very graphic and much more emo-like. It is almost to exaggerate the type of sacrifices that destruction characters like the guardian yaksha Xiao make to buff themselves. It must be clarified that this kind of self-sacrifice is different from suicide. Perhaps the first thing that must be emphasized about destruction characters is that they have great survivability. They can live and survive. That is the first most important thing. When they sacrifice something, like their health or whatever, they are not offing themselves or committing suicide, they need to live first to tell the tale and then turn that sacrifice into increased damage. The moment you go into suicidal territory, you die and lose the game. The path of destruction is dangerous and can result in getting killed. That is what makes it high risk high reward.
When Blade consumes his hp, he will never commit suicide. The most that will happen is that his hp will drop to 1. Same thing with Xiao: his hp decreases until it hits 1, at which it will stop decreasing.
Committing suicide ('offing oneself') is the act of an idiot. The dao of destruction is completely different. You have to be smart to know the difference between suicide versus survivability and sacrifice in exchange for buff. Even if you suffer a huge failure in life or you suffered a great loss to bring down your enemy, as long as your hp is above 0, you have not yet died and can still survive. As long as your enemy is dead and you are still alive, it almost does not matter how much hp you lost. You can recover it and live to fight the next battle. But if you die and lose, it is game over. The sacrifices you made almost become meaningless and not much different from suicide in that case. Not everybody can walk the path of destruction and live to tell the tale.
Destruction characters almost need to compensate for the risk of dying by dealing more damage than normal. That is why destruction characters like Xiao or Itto have high innate motion values, while taking a risk of sacrificing some superfluous attribute. But they can hedge this risk by being tankier or possessing greater survivability than normal (Xiao can jump to avoid attacks like Freya in FF9, and Itto has high defense and can shield himself as a geo unit).
What exactly does Itto sacrifice again? Oh yeah, during his burst he reduces his damage resistance. But this is almost like a cheatcode since as a geo unit he will be shielded much of the time, and because he has high innate defense he can tank a ton of damage like a sponge anyways.
If you are more conservative or do not like taking risks, perhaps the path of destruction is not for you. They are plenty of non-destruction characters that do not make such self-sacrifices but still deal a ton of damage, such as Cyno.
In Genshin, Blade will probably be an anemo sword user. But he does not have to be. The idea behind his kit does not really depend on his weapon class (or even element for that matter).
Blade's E sacrifices his hp while entering the hellscape state. While in this state, he buffs his damage bonus (or can give another multiplier like Yoimiya or Scaramouche's E). Moreover, in this state, he gains anemo infusion, and his NA/CA have increased aoe and will consume part of his hp (icd say every 0.6s). And when dealing damage against enemies with less than 50% hp, he can heal himself with his NA/CA (as Genshin does not have a toughness meter for all enemies, unlike Star Rail). His attacks scale with his atk and hp (dual like Dehya). This state lasts say 10s and has say a 6s cd.
Blade's Q does an aoe nuke on the enemy, scaling with his atk and hp. It deals additional damage based on how much hp he has lost so far.
Blade's passive gives him 1 stack of charge every time he sustains damage / loses hp. Once he has 5 stacks, he will unleash an extra aoe attack that also heals him. Effect can trigger while he is off-field (this is optional, but can turn him into a subdps too, especially with damage sharing or corrosion). And name this passive after one of Genghis Khan's other descendants. He had many, so there's no need to play favorites. Let's call this passive Chagatai's gift or Ogedei's gift. It sounds more powerful and pleasing to the ear, just like how Morax sounds more godly and appealing than zhongli.
Speaking of Genghis' progeny, in a game called Genshin/Yuanshen, where on earth is Ogedei? Chagatai, Tolui, Jochi, Kublai appear to get some limelight in the game in one form or another (e.g. baizhu, dottore, etc.), but how about the 2nd great khan of the Mongol empire Ogedei?
There is also some rumor that jochi had more recorded progeny than Genghis' other sons, but that is written recorded history and may be because of historical bias from the Ming dynasty. The Ming was notorious for 'cooking the book', writing extremely biased books and fabricating fake stories to make political attacks on the masses while advancing the interests of the few.
The reality is that Genghis' other descendants probably had just as many, if not more progeny, as jochi. It is just that it was not as much recorded since the Ming dynasty was only concerned in writing more about jochi to justify the rule of the house of zhu. And to name your son jochi despite the history of chu: that is such a chad move expected from the great Mongol khan Genghis. It is a big middle finger to history and the heavens. It takes balls to name your eldest child after the people who killed you. But perhaps that is why Genghis is famed for having the most descendants, spread around the world, of any conqueror in history.
Blade's eidolons in Star Rail seem more similar to Scaramouche than to Xiao or Itto.
Blade's e1 gives his burst bonus scaling in single-target situations. His e2 gives him 15% cr while in hellscape mode. With his e4, when his hp drops below 50%, his max hp increases 20%, stacking up to 2 times. His d6 can reduce the max stacks from 5 to 4, while giving his extra attack some bonus scaling.
These are fine and dandy, definitely better than hu tao's constellations, perhaps even meta or broken, but maybe we can elevate this to god status like Xiao or Itto's c6?
In Genshin, Blade's c1 can give him more anemo dmg bonus based on a percent of his max hp. His c2 can increase his crit rate by x% every time his hp changes, stacking up to y times (can also buff crit damage or both cr and cd). His c4 increases the hp of all party members each time his hp falls below 50%, stacking up to 2 times. His c6 reduces max charge stacks from 5 to 4, gives more scaling to this extra attack (or even extra crit dmg), and gives each of his NA/CA a 50% chance to generate one extra stack.
Xiao is the premier destruction unit of Genshin and one of the first destruction units released in the game. Now Blade is almost filling that same spot as an anemo destruction unit that sacrifices hp. In fact, Blade is almost like a cross between Xiao and hu tao.
But anyways, one abundance unit that works with Blade is Luocha. Luocha is an imaginary support. Imaginary has similar color style as geo in Genshin. So the duo of Blade-Luocha in Star Rail almost mirrors the anemo-geo duo of Xiao-Morax in Genshin.