Hagakure and Leon are more oblivious than Mondo and Taka, and that's problematic to say the least. The two had been going on dates for a few months without even knowing they were going on dates! It wasn't until Maizono brought up their relationship did Leon and Hagakure notice they were dating. Like, they KNEW they had gain some romantic feelings for each other, they just didn't know HOW! Like, this is how they officially became a couple:
Yasuhiro: Yo, are we like, dating?
Kuwata: I mean, like, are we?
Yasuhiro: I mean, like, I wouldn't mind dating you bro.
Kuwata: Bro...
Maizono: You two have literally been going on dates with each other for MONTHS now! How do you two not know you're dating?
Kuwata: *Sudden realization hits him as he turns to Hagakure* Bro!
Yasuhiro: Bro!
Kuwata: I mean, do you want to be my boyfriend?
Yasuhiro: Yeah! I'd love to be your boyfriend dude!
Kuwata: Yay!
Maizono: *face palms*
And that's how these two idiots officially became a couple. Or, well, more accurately realized they were basically a couple.