This is basically a classic pushy male lead + innocent honor student female lead premise, with the associated problems therein. However, this one does indeed have an unusually mellow feel to it.
It helps that the heroine appears to be enjoying herself very much. Being an otherwise overly self-sacrificing hard worker, she seems to be having fun with her new, exciting, rosy school life. The very pretty art includes a variety of rather quite lovely expressions from her -- she maybe a serious class rep type, but her coy smile (see: chapter 1) and the fall-in-love-with-me expressions (every chapter since) are seriously dangerous. :/
The male lead is also slightly, just slightly, unusual. On one hand he appears to be your standard handsome-but-handsy shoujo manga bad boy (sigh). On the other hand he appears at times almost lacking in confidence, mystified that she keeps coming back despite his repeated efforts to push her away. Of course, to the heroine -- and the reader -- his tsundere antagonism barely hides a series of actions that include: diffusing delicate moments with classmates by putting negative attention onto himself, teaching her how to relax and chill, protecting her from unsavory people, leading her around an adventurous, fun day out, and generally being her very own special prince...