Only in the park do these two talk to each other as equals. It was only after they had a serious conversation (about the aspiring high schooler) that Otori asks something like this:
"Ne, what do you see me as? A father figure?"
Hoshitani shakes his head, "You're too young to be my father. Besides, if you were, you'd probably be the best dad ever."
Otori smiles at that, "What about a brother, or a friend?"
Hoshitani smiles, "You're more than that to me."
Otori contemplates, humming for a moment before asking, "A boyfriend then?"
He is only met with silence for a whole minute, seeing Hoshitani blush. "O-only if you want to," he stutters as he turns away.
Blinking at that, Otori slightly blushes too, "Are you really OK with that?"
Hoshitani silently nods, blush still on him.
Otori pulls him into a hug, "OK! I'll be your boyfriend," he says before pulling away, an arm still around Hoshitani's waist.
Hoshitani's blush gets brighter though as they look into each other's eyes, seeing themselves reflected in them. "Yeah..." Hoshitani breathlessly says as he closes his eyes, leaning into Otori.
Otori leans down and kisses him on the lips, innocently and gently, like a butterfly's kiss, before pulling back.
They both smile, then Hoshitani runs off, "Bet you can't catch me!"
Taking that as a challenge, Otori replies, "Get back here!" Then he runs off after him, the both of them laughing into the sunset.
Thus, they finally become boyfriends.