Lum Invader

Lum's a sweet, innocent, faithful, and good-natured girl, but she can also get jealous and get hot-tempered, usually due to Ataru and his incessant addiction of flirting. However, in early chapters of the manga and at least till the start of season 2 of the anime, Lum had a nasty streak, almost antagonistic towards many of the characters. She even hatched schemes to be with Ataru when Shinobu was involved.