Long story short:
Girl in the middle of the OP image (short orangish hair) was a dude who got hit by a spaceship and killed. The Aliens brought him back to life, only they turned him into a girl.
He was basically ok with this, and the girl he had a crush on who rejected him suddenly wanted into his panties, as does his Tsundere childhood friend.
He was a really faggy boy anyway, so it was a net improvement in his life.