Ah..."Just Once", except it never really ends after just one time, does it?
But I must say...GREAT ENDING! I love it. Indeed, Marriage is something that you should only do once, because you two will stay married after just one, yes?
And marriage is always one of the best ways to end a sweet Vanilla release. I like how she expected him to ask for something else and just replied despite his earnest request to marry her.
"He ('Senpai') who Perseveres To The End, will Get Laid." (lucky bastard) ... and even get bold enough to propose afterwards. And (if I get the wording right) a "kuudere" Yamaoka-san, even if at first she "doth protest a bit much", is fine, too ... seemingly, his sincerity seemed to have flipped her switch, or she really didn't see an offer of marriage coming.