The reactive healer: Luocha (LC) is a healer that reacts to when characters fall below a certain hp threshold. When he gains 2 stacks of abyss flower, he deploys a field. When the field is active and characters deal damage, they heal the whole party. As of version 3.8, Luocha has no analog in Genshin. When Jean uses NA she can heal the whole party. When Mika uses his Q, he grants an effect where characters' NA heal themselves only (not team). But there is currently no healer that allows all party members' NA to heal the whole party, without needing Q, and that applies to whenever damage is dealt, not just NA.
Luocha's eidolons are actually some of the best seen for a support in a while, combining harmony, preservation, and nihility. E1 makes field give atk buff. E2 allows Luocha skill to give a shield at a certain hp threshold (scaling with atk). E4 reduces enemy atk. E6 (the dust eidolon) makes burst reduce all enemy res by 20% (for 2 turns).
The E6 seems to nod to Morax in Genshin. The difference is Luocha needs E6 and burst energy cost, whereas Morax can just use his E and have 100% uptime. So it is not that Luocha's eidolons are broken, but that they flow and progress well for a support, making Luocha convenient to have in the party (but not a must).
In fact, an E6 Luocha is actually somewhat similar to what a C0 Morax with Tenacity (atk buff) can provide. The difference is that Luocha heals a lot more.
C6 Morax also provides 'reactive' healing, but that is when the character gets hit, whereas Luocha heals when the hp is below 50%. Luocha's healing is probably more useful than C6 Morax's healing since in Genshin it is possible to fall below 50% hp without getting hit (e.g. corrosion, self hp drain/sacrifice).
Now imagine creating a Morax-like preservation unit in Star Rail. Using skill gives all allies a shield that reduces all enemy res by 20%. And the shield lasts at least 2 turns. And the E6 effect is: when shielded characters are hit they are healed.
A Morax-type unit would most likely put Gepard and March 7th out of business. But given Gepard is on standard and March is free, introducing such a unit into the game may not be too farfetched of a possibility.
Luocha tends to work favorably with the destruction path as well as characters that use a lot of follow-up attacks (Jing Yuan, Himeko, Svarog).
Luocha should be able to fit on most teams as a general healer. But there are some characters where Luocha may have antisynergy. These include characters like Arlan that rely on having lower hp to deal more damage. It is similar to how hu tao has antisynergy with healers in Genshin. The thing with Luocha though is that he automatically heals when hp gets low, whereas in Genshin at least one can choose to abstain from switching to the healer.
A simple idea for making a Luocha analog (call it LC) in Genshin could be: whenever a character's hp falls below 33%, LC heals that character using whatever formula and gains 1 stack of abyss. This effect can be triggered once every 10-15s. Healing will also remove any debuff on that character (Genshin currently lacks as many debuffs as HSR). It can do so by applying geo to the character.
The E skill has a similar effect, providing healing to a chosen character. In Genshin one cannot usually select which character receives the healing, but one can try to make an effect where the healing occurs after 2s to whichever character is on-field, giving time to switch to another character if needed. Otherwise one can do a healing over time like Yaoyao / Barbara / Kuki E. Another idea is to make Luocha's E create a special crystal drop on the ground (like a crystallize shield or bloom core). A character can then pick up the crystal and gain the healing.
Using E (including automatic E) or Q will grant 1 stack of abyss. Once 2 stacks of abyss are obtained, LC will deploy a field / grant an effect to the team where whenever any party member deals damage, they heal the whole party. This effect can last 10-15s. And then LC's Q can debuff the enemy while dealing aoe damage.
Ok that's cool, but is there a need for this kind of healer when characters like kokomi and baizhu exist? Maybe. In Genshin, LC could probably be one of the best healers for someone like Xiao, hu tao, or perhaps even some new characters. But then why use Luocha over someone like Bennett? Maybe you would not, but if you are using Bennett on your other abyss team, Luocha could be the next alternative healer.
The real differentiator from other healers would be the constellations. Let's translate some of Luocha's eidolons into Genshin. LC's C1 makes the field give a 20% ATK buff to the whole party. Ok that is fine. Many characters' C4 provide some stat buff to the party.
LC's C2 makes his E crystal give a shield to the character. The C4 reduces enemy attack (like one of Qiqi's constellations). The C6 makes his Q shred all res by 20% (so basically what Morax does at C0).
Such constellations would be very balanced (good or great on the constellation scale) by Genshin standards, while also significantly powercreeping kokomi and baizhu's constellations.
For someone like Xiao, a C6 LC would probably be equal to or a bit below a C5 Bennett as a support. The real differentiator is that Bennett gives a much bigger atk buff than LC, while LC provides some more defensive abilities. As stated above, Luocha's buffing abilities at E6 are comparable to what a C0 Morax with Tenacity provides, so Luocha would not be used to give the biggest buff in the game, but rather a healer and defensive unit. But to be comparable to Bennett as a healer is already something few characters can achieve.
But honestly, Xiao's hp drain is not too large, so Xiao does not need a healer as desperately as someone like Blade. That is why LC would be a much better support for a character like Blade that sacrifices large amounts of hp at a time. But as of version 3, a Blade-type character does not exist in Genshin (Blade is actually very different from hu tao, and hu tao would not benefit that much from a healer because of the under 50% hp buff she gets). But if a Blade-type character ever releases, then a case can be made to create the analog of LC in Genshin, to completely powercreep baizhu and kokomi and make them absolutely useless.