Hmm... So considering chapter 0 I expect to be basically reading "Hentai with plot." But like. It's pushing the limits of my acceptance that "Heal" can do this many things.
"Heal" seems more to be a derivate from a more primordial and OP ability that let's teansform things at the cost of having to know all the memory of everything you use it with.
Based on how his power was described it seems to basically be a combination of 'Overhaul' and 'Rewind' from BNHA, except you experience everything you rewind and keep some of that memory. In other words, it's fundamentally actually not a healing power. However, in this medieval fantasy world with heroes and battles with demons, this power only manifests during a war- and the most obvious use for 'rewinding' individuals is of course healing.
So, basically, the only reason he's called a 'healing hero' is because nobody in the kingdom had the obvious(for a scientific civilization like us) idea to try and find out how this worked or whether its boundaries could be pushed. I mean, since all the other skills and powers run on mana, not reliving experiences, so it's clear 'heal' is not actually the primary skill of this power.
TLDR; this could all have been avoided with SCIENCE!