The song is titled 'Ii Yu dana.'
There's also a version of it sung by the female cast of the Love Hina anime: https://www.youtube.com/watch?v=dEfuAwiHwE4
Did he not see the opportunity to "tease" her back by accepting the invite? No matter if she was being serious or not, accepting the invite would have gotten a blush out of her because it would have been the unexpected reaction. Get your shit together, Nishikata! You can win this thing! Chi is...
Chapter 22 of Clueless Transfer Student seems incomplete at only 4 pages long. Are there more pages of that chapter that just didn't get uploaded for some reason?