S1·E5 The Coming of Rei the Handsome Shapechanger!

This show features the first appearance of Rei, Lum's former fiance. This episode opens with Ataru in his room watching a storm, and Lum trying to coax him to bed. Shinobu meets Rei and brings him to Ataru's house. After a lot of arguing, Rei challenges Ataru to a duel for Lum.