Tentacle Girl

A man becomes a tentacle girl? Placed in a boss room of a dungeon? Forced to face adventurers? What's going on?

*** Warning: While rape doesn't happen in the story, it gets talked about and referenced some, due to it being part of the setting, and it may sometimes be attempted. ***
*** Warning: Sex involving both men and women and the main character does eventually happen (though it takes longer than I expected). **