Okay, so from what I've managed to piece together, this can be a little tricky because 'Blank the Series' the show is based on a novel called 'Make It Right'. The main characters are basically the same, but the novel dives a lot deeper, especially into Fuse and Tee's history.
You've got Fuse, the swim team star who's kind of closed off after a past incident with his childhood friend Tee, who ghosted him. Then Tee returns, desperately trying to reconnect and fix things. The novel really spends time in both their heads, showing how much that separation hurt each of them. Frame is another major one, Fuse's teammate who acts as a catalyst for a lot of the drama, kind of stirring the pot between them. There's also a character named Nan, who's Fuse's ex and adds a whole other layer of complication and jealousy. The novel gives her more motive, I felt, than the show sometimes did.
The heart of it is Fuse and Tee trying to navigate past trauma, present misunderstandings, and whether they can actually be 'blank' slates with each other again. I read a fan translation a while back and it's way more angsty and internal.