Ideas in lieu of an actual story
Which is why she needed him to save the girl. monsters feed off heightened emotion, but given how they perceive threats, that emotion must be harvested from children as adults will question their emotions where children just accept them.
Tower of the Serpent
Hours ago he would've felt sick from the mere thought of eating out this female monster, but now he couldn't remember why. he was in heaven.
The Huntress and the Monster Prologue
Without any female monsters around naruto was probably incredibly backed up, more so than any human could be, apparently.
Castlebabes - A Castlevania parody with monster girls
Before him in the middle of the cave was a giant female monster. she put the slime sisters' combined size to shame. just her laying on her back forced naito to look up at her.