Kanzen Kaihi Healer no Kiseki - Vol. 7 Ch. 31 - An Unexpected Visitor

[MangaDex]

 

[Xeroxcopy4free]

kinda reminds me of naruto early days, even the entrance is the same except the water is a holy drink that boost your chakra.

 

[PLaci1982]

My guess is that the fairy is either affiliated to the demon king, and/or the subordinate of the demon king, or the demon king itself.