something with tentacles?
Depends on how ok you are with fetishes because I know a few hentai mangas that have tentacles with consent but they don't turn into a hot human lol.
Ok I'm suggesting anyway:
BL (?????)
Tentacle experimentation, mind break, urethra insertion.
https://myreadingmanga.info/buranran-ishiki-takai-kei-insei-shokushu-shidou-ochiyuku-pride-eng/
Established couple encounters tentacles in the wild.
http://www.mangago.me/read-manga/hot_summer_star_vacation/
Strongest knight gets one-upped by a yaoi fangirl who controls tentacles. Rape.
https://myreadingmanga.info/mentaiko-entwine-english/
Straight
Married to a tentacle monster that can speak, they have sex for the first time. Sex marathon, multiple penetration, unexpectedly fluffy cuz they get a child later lol.
https://nhentai.net/g/213578/
A proud knight encounters a tentacle monster in a dungeon but it doesn't know how to utilize its strength to 'defile' intruders. Fed up with how lacklustre it is, the knight teaches it how to have sex. Consensual all the way lol. They end up teaming afterwards.
https://nhentai.net/g/112597/
This is a weird one. It's got all the strangest fetishes but they don't actually fuck. They're like incredibly close INCREDIBLY close friends. It's got the eggs thing, stomach inflation, unbirth, lactation, just a lot of 'kinks' but it's so weirdly wholesome. Emphasis on weird.
https://nhentai.net/g/186780/
Please recommend anything similar to it, whether it be straight or bl.. please gimme ;-;