Ieshige Tokugawa

He was introduced in ep.6 as the eldest son of the 8th Tokugawa shogunate, he somehow lacks any physical prowess, but makes up by being studious. He wears a noh mask to hide his emotions and his disgust for all the lies that he experiences around him, because of his persistent for knowledge about the giant insects he secretly tries to intrude into the Insect Magistrate's Office under the name Nagatomimaru to access the Momijiyama Archives only to to be caught by Kotori, a deal was made after the latter found out who he is.

He somehow develops an affinity towards Jinbei.

(Source: ANN)