He found himself an SSR GF. Cute, shy, kind, ero-ero to the point of bursting. Man, this was one of those "can't get enough of this shiet" works. MC should waifu her immediately after graduation.
The Flower's Nectar must taste like some sweet Vanilla, yes?
What a sweet girl, so shy and yet so devoted to her boyfriend that she'd have sex with him on his birthday...And then come to like it that it becomes a pretty regular thing.
Hmm...I wonder if his friend knows, and is just playing along with them.
That ending though. Hmm...I think having pictures like that is fine, but maybe not the best idea to be viewing them where others can easily just peek and see what's there.
It's probably too obvious to suggest it as a tag but virtually all the males in school no doubt regard Haru-kun as a "Lucky Bastard", for winning the heart of Kanna-chan ... and, to be blunt, for being "the one" who will get (a-hem) sexy time with her.
Could be that Tanaguchi 'knows', or at least suspects, but he seems willing to keep it quiet.
That aside, you no doubt know what you have to do, when you both "come of age", Haru-kun. Do Not Resist - It Is Your Destiny!