If you're looking for manga similar to Mobile Suit Gundam-san, you might like these titles.
Earth is under attack. As giant monsters destroy the cities and alien warships swarm across the skies, 12-year-old Takuma Ippongi runs around the rubble trying to save himself and Koyori, his girlfriend. Takuma's character flaw that he's too hyper and has no self-control and always does everything too hard. When Koyori's sweater catches on fire, Takumi whacks her on the back to put it out, but he hits too hard and hurts her back. "I was just tryin' ta put out th' fires!" he apologizes. "You could've done it gently!" she says. "Why are you so reckless? You've got no self-control! You can't always use maximum force!"
A 4-koma manga that re-imagines the anime's title character Lelouch Lamperouge as a part-time convenience store worker.