Komugi is the official Neiro and Cocoro's brother, confirmed by riko wako mama on her official ig page (https://www.instagram.com/p/DJ7tc1ATcxs/?hl=en&img_index=1).

As we all know Neiro is used to get called Iro-chan by his family and Cocoro as koko-chan.

Also our Komugi has a "family-name" and it is $MU-chan!