Injuu no Datenshi: Requiem for Fallen Angels

Hero lives with a lovely younger sister and suppresses affection for her. However, his friend knows of such feelings and invites hero to attack surrounding women. But hero has a subtle feeling that his sister is going to be involved as well sooner or later...

Despite "injuu" in the title, there's not a single tentacle. The work is of insult nature, but among all that ruckus there is also one romance route.