Katsura Kotaro is a good friend of Tatsuma Sakamoto.
In his life, he has made four most important good brothers, Katsura Kotaro, Takasugi Shinsuke, and Sakata Gintoki.
Sakamoto Tatsuma felt that his occasional resolute dive back to Earth was caused by lovesickness from time to time. Although he said it was a bit hypocritical, it was precisely his three good friends who made him close the door and thank guests every time he returned to Edo.
However, something like the door, Takasugi Shinsuke said, is just like a decoration like Gui's brain.
Conception: