Odazai

Odazai  is the slash ship between Oda Sakunosuke and Dazai Osamu from the Bungou Stray Dogs fandom.

Canon
The meeting between Oda Sakunosuke and Dazai Osamu still a mystery.

The relationship between Oda and Dazai, is inserted over a period of time of Bungou Stray Dogs called Dark Era.

In this arc of time, the young executive Dazai seems to care a lot about his only friend, except Ango Sakaguchi, Oda.

Their relationship takes place in the anime, manga and the Dark Era Novel, written by Asagiri Kafka.

Anime
In the anime, Dazai and Oda, along with Ango, are used to drink together at the Lupin. However, it doesn't appear Dazai drinking what he ordered, he only talks to Oda and Ango. Sakunosuke, during his meeting, has declared that he finds Dazai really interesting, and Dazai has replied with "No way, you're more interesting than me!". Plus, Dazai refers to Oda with the nickname "Odasaku", which is in Japan a nickname for only close friends or someone who is in a close relationship, Osamu calls only Oda with that affectionate nickname.

When Oda is around, Dazai seems to be happier and his facial expressions soften in a sincere smile.

Fanon
A lot of people from the fandom believe that Dazai was actually in love with Oda. Not only shippers. Additionally there's a lot of hints telling that it might be a true theory. But we can't be 100% sure yet, since - as it's kind of written in the canon section - some of the things about their relationship are still a mystery.