For one reason or another, when he confesses to Sanae, he gets a no! But she says it's okay to be more than friends.
From there, he is pushed around by Sanae's flirtatious behavior. Will it develop into a romantic relationship?
Sanae is so cute! She's so cute!

This is the 1st of the series, if we go by the listing on Toranoana.jp

The series seems to go:

1. Koibito Sanae-san -I Luv U-
2. Koibito Sanae-san Plus
3. Kochiya Sanae no Yuuutsu Aki-hen
4. Sanae-san wa Ichi ~Yaichashitai~
5. Sanae-san no Tawawa ni Tsuite
6. Motto!! Sanae-san no Tawawa ni Tsuite

Of these, only the 1st (this one) and the 6th have been translated at the moment