Prince from Slut Planet

1-3. Fushidara-sei no Oujisama (ふしだら星の王子様)
One day, a suitcase crashes into the ground in front of college student Jin Terano. Pike, the boy who's sleeping in it, is an alien who has come to destroy the earth. To stop Pike, Jin must show Pike something more fun than destruction. However, no matter what he tries, nothing works. Giving up, Jin comes up with the last thing he wants to do in his life: have sex.

4-6. Kara no Kago (殻の籠)