Lemonkane

YamaAka is the slash ship between Aoi Akane and Yamabuki Lemon from the Toilet-bound Hanako-kun fandom.

Canon
Yamabuki and Akane are shown to be on fairly good terms with each other and are often seen hanging out together despite Akane having a small grudge against Yamabuki for Aoi thinking that Yamabuki is attractive. Akane commonly asks and uses Yamabuki for practice with confessing to Aoi (Despite him confessing to her often) However due to Akane's bad wording and gestures it often comes off as him asking Yamabuki out and confessing his love to him rather then Aoi. Yamabuki seems to be aware of this and often teases Akane for it. It is a common running gag in the series about Yamabuki having a crush on Akane and vice versa.

In the Confession Tree Arc, Yamabuki helps Akane practices confessing to Aoi under the Confession Tree. As a result, they were turned into a lovey-dovey couple for a short period of time due to the rumor attached to the tree and they confirmed that they were dating. However after the affects of the tree wore off they both seemed to forget about it clearly confused. During this time period Aoi was extreme conflicted since at the time she said she didn't like Akane back but was wondering if Yamabuki was more attractive then her and bringing up that Akane and Yamabuki were getting closer recently.

After that the two continue to hang out and Akane continues to ask Yamabuki out and he starts practicing romantic pick up lines with Yamabuki for Aoi. It is later brought up that Akane is one of the few people Yamabuki bothers to interact with due to him not really caring about his surroundings and often not noticing serious things such as the academies time jumping forward and some students start growing older.

Fanon
The ship sailed as a result of the two's strong friendship and Akane being one of the few people who Yamabuki bother's to notice. Another reason the ship gained popularity was because of the Confession Tree Arc and which Akane and Yamabuki end up together romantically even if the two weren't fully aware of what was going on and they broke up soon afterwards they were still together romantically even if it was for a short amount of time. The running gag in the series where Akane keeps accidentally messing up his words to make his confession to Aoi go more towards Yamabuki also helped fuel the ship.