Historically, the Maru-Yu submarines were of a highly unusual design, and initial tests failed to get the prototype Maru-Yus to actually submerge, causing many Maru-Yu jokes to involve her only managing to get her head underwater while her legs still flail above water. Kiso was nearby in the test runs, and Kiso's crew made jokes about the Maru-Yu's strange shape, causing some artists to treat Kiso as some sort of senpai to Maru-Yu because of it.
