recently I finished a chinese One piece fic where the MC training was haki cultivation style. He created dantian and everything. When he broke through he could even fly like god damn son goku. Another one I read was naruto fic where Mc did the washing the bone marrow thing to live longer. Are there any similar fanfics with MC pulling cultivation out of their ass dor the setting they live?
Just go find random CN fanfictions. Most of them will eventually turn into your average Xianxia novels. They only used the Anime setting to bait people, in truth those are just your random Xianxia novels with Anime characters.... And eventually it isn't even an "Anime Fan-fic" anymore since they made more Original Contents and just get rid of the Anime contents....
https://www.fanfiction.net/community/Naruto-Xianxia-and-Xuanhuan/129742/ you can found most Naruto and cultivation fanfic on the above link Actually, it just depend on which setting the fanfic took, you can expected more cannon if it took the anime world setting
Based on your preference, the only I think that fits is Nurarihyon System in Another World. One of my favorites