Sakoo

Yotou is the slash ship between Yokoo and Satou from the Toilet-bound Hanako-kun fandom.

Canon
They are seen together almost all of the time, a pair, that should not be separated. They sit next to each other in class, eat together during lunch, are seen celebrating an Old Man Party during the Three Clock Keepers Arc, study together, come to class together, are in the student committee together, and are generally always together. The only scene I can think of where we see one without the other is during episode 8, or the Mitsuba chapters of volume 4, where Yokoo explains to Kou about Mitsuba.