宿り蟲 ～僕が触手で触手が僕で～

Quiet main character has always been a target of bullying. One day he picks up a tentacle seed fallen from the sky. Next day he is visited by devil girl Lilim who makes a mistake so that tentacle merges with protagonist. The only way to get rid of the tentacle now is to attack women to create enough energy for a new seed to emerge...

[From vndbreview]