Tenchi Universe S01 E10 No Need for an Arch Rival!

A ruthless interstellar bounty hunter, Nagi, arrives on Earth to claim the price on Ryoko's head. She kidnaps Tenchi and challenges Ryoko to a showdown to claim him back. However, she doesn't reckon on her spaceship cabbit, Ken-Ohki, falling in love with Ryo-Ohki!