You’re forgetting everything outside of Kotori’s route. Yoshino looks up to Kotarou’s bravery, looks down upon how Kotarou treats people as entertainment, and both respects and trusts Kotarou in most cases.
Who tried to helplessly run into a fire to help Kotarou? Yoshino. Who risked his life to inform Kotarou of Asahi’s curse? Yoshino. Who supported Kotarou and Akane’s struggles in the new world? Yoshino. What is Yoshino’s biggest goal in life? To be who Kotarou is.
The only time they ever clash is in Kotori’s route, in which Kotarou abandons Kotori (his best friend) and tries to continue life as if nothing happened. Yoshino saw Kotarou as his companion. They both have their own groups, but at the end of the day Yoshino, Kotarou, and Kotori are the three lone wolves of Kazamatsuri, and there is a trusting bond that comes from that. You don’t abandon your pack… Kotarou did exactly that… But when Yoshino saw an injured Kotarou with Kotori at the end, he ran to their side to support them.
Buuut as a teenager living in England, the biggest sign of friendship is an insulting standoffish greeting… and then comedy.
