Supreme couple. My boy is gonna go for it, even calling her by her first name. Very proud.
Natsumi's interest in those that do their best may stem from the encouragement she received from Igarashi-chan back when they were in school and she couldn't give her chocolate to a guy at the time shown in the Ch. 58.5.
I'm always impressed how even with such short chapters the author manages to balance development among all the side couples along with the main well.