It's cute and all but... She's flirting really hard and there's no explanation for why she's so into him. It kind of bothers me. She even sat on his lap in the second chapter, of all things.
I just got finished reading Giji Harem, so I can't help but compare this with that. In that one, the senpai is a cool and experienced guy, has a cheerful personality and half-flirts with her, and the kouhai isn't some class idol type, she's just a little shy yet very expressive, so the dynamic makes perfect sense.