Koutarou and Rinko go way back—they were traveling biologists together and were actually there when Rinko discovered that Kaiju skeleton and decided to smuggle home an egg. He kept her secret, though he's never really approved of how she ended up raising Kuroe. Still, he's genuinely protective of the kid, acting more like an uncle to her than anything else. This protective vibe was strong enough that Arata once got the wrong idea and thought he might be Rinko's boyfriend.
These days Koutarou works for the Japanese government, which has put Rinko on edge. She's worried about what it means for Kuroe and her newly hatched sibling—all she wants is for them to be happy and safe.
Content compiled by AnimeList.moe from publicly available sources.
