WARNING - There is tentacles sex
Japanese Title: 中海義影 - 退魔捜査官アヤノ
From: Insult Anthology Comics - Tokiryoujoku Vol.33 (p97-112)
Description:
A female heroine goes to save two from being attacked by some kind of jellyfish monster. However, it's just a ploy for the monster to have sex with her because the men are being controlled by the monster. The breast expansion is just a before and after shot, which takes place after the monster has sex with the heroine but still better than nothing I suppose.
Complete Scene
http://www.megaupload.com/?d=02GPLUG8