The first genuinely romantic moment of the series, which stands out by its contrast with the comedic weirdness that tints most of the series' romantic moments, happens in chapter 12 of the manga and the second part of episode 1 of the anime. Yamada and Kosuda are walking to Kosuda's house while sharing an umbrella held by Kosuda. Kosuda accidentally hits Yamada in the head with the shaft of the umbrella a couple times, and she starts to get annoyed, but then she notices that it's because he's favoring her with the umbrella so much that his far arm is getting soaked. Upon noticing, Yamada silently reaches up to nudge the umbrella into a more balanced position, and thinks to herself that she hopes Kosuda's house is far away.
At the end of episode 12, Kosuda and Yamada finally become an official couple.
In chapter 280, Yamada FINALLY confesses she loves Kosuda in public. In front of the entire class. Also doubles as a Crowning Moment of Funny, because as soon as she realizes what she's done, she dives through a third floor window in embarassment.