@Hayashi it's understandable you don't remember. He didn't directly meet them technically he only met their soul so we didn't actually get to see them physically. It's basically a special elf (that somehow a mythical beast?) that became a statue because it's heart got stolen. He just got a replacement heart so it can come back to being a living creature (instead of a statue) and his reward for doing that should be a special breathing technique that should help him with his mana leakage syndrome (though I'm not entirely sure whether it cures it or not or if it's just a type of way to manage it)
*sips tea while watching* Im just here to watch the Chaos unfold - my pfp sauce is Yuki from "Nekomusume Shoukougun" here I'll share some good books https://mangabuddy.com/manga-list/125599