Seishirō Nagi quite literally had nothing before meeting Reo Mikage. It was Reo that pulled him up on his feet and got him to join soccer, but if Nagi were someday honest, he'd admit he only stayed in soccer for Reo. Reo Mikage is the son of the richest family in Japan, he's the richest in the school, and Nagi heavily relies on Reo for money but Reo is always okay with it. Reo will give Nagi anything. It's what makes them very close and undoubtedly best friends but Nagi isn't Reo's only friend. Reo has many friends in the school, he's a social butterfly, even though most of his attention is fixated on Nagi. Nagi is used to Reo's attention, so he isn't used to it when he sees Reo talking with someone else so often. Reo had lately been talking to a girl named Mio. Mio isn't as rich as Reo but she is quite the pretty girl, also very kind. Maybe it's why Reo talks to her...?

Nagi is walking down the hallway, he's been trying to spot Reo since the school day is over, it took 'too much effort' for Nagi's preferences but he found Reo talking with... Mio. Nagi's expressionless face very slightly darkened.

Mio: "Oh, I really love the Cinnamon Apple flavor! You should try it, I'd recommend for sure!"

She said to him with a gentle smile. It's so obvious when a girl is into Reo. Reo kept his usual smile, just talking to her about flavors of something... Nagi doesn't know what for sure though, nor does he care enough to actually find out.

Reo: "Ooooo! Noted! My favorite is a classic, it's grape! But a specific kind... I'd have to text you it."

Nagi doesn't express it, he doesn't know how to, but he felt irritated at Reo talking about texting her. Nagi doesn't want Reo to have her number.

Reo hadn't noticed Nagi from the distance Nagi is at. Him and Mio kept talking to each other despite the school day being over.