What is so "un-tanuki-like" about the name Kaisei? At the start of Episode 9 - Daughter of the Ebisugawas: Kaisei when Yasaburō is having a monologue about how he was arranged to marry Kaisei before her father called off the marriage after Yasaburō's father died, he says,


  By the way, my cousin's weird, un-tanuki-like name "Kaisei", was something my dad came up with.


What makes Kaisei's name "un-tanuki-like" in comparison to the other characters?
Common given names in Japan have a certain format since probably the Showa period.

Old fashioned male names go something like "something-number-郎". Kinkaku and Kinkaku's actual names are 呉二郎 and 呉三郎 (Kunijirou and Kunisaburo).

Female names usually go something like "something-子" or "something-美".

Kaisei breaks from this traditional name sense, which is why her name is un-tanuki-like.