As more or less Rokuna's boyfriend, he got involved with Ichirobei's scheme right away, recruited as a Mon Colle Knight along with Rokuna. He fits into the role fairly quickly after overcoming the shock of the parallel universe and the silly outfit he'd been given. Like Rokuna, he hopes to find the items to unite the worlds. Determined and with a lot of endurance, he provides the strength of the team. He's got a particular love for dragons, but is most commonly seen with the (initially chibi) Pegasus he met early in the series.

Mondo sees the world through Moe glasses. When confronted with cute girls, especially the sort that seem to needs help he switches to hero mode, sometimes taking his shirt off in the process. Unfortunately, the girls aren't really in dire need of (emotional) rescue and Rokuna tends to violently bring him back to reality.
Hence, Mondo's constant flirting with others girls isn't so much that he doesn't care for what Rokuna thinks, he simply can't help himself.

Nothing's known about Mondo's home life in the human world, though as the series progresses he more and more seems to live with the Hiiragis.