So here's my theory on why Nene likes Yamada, based on what we currently know, so spoilers and lots of speculation on my part. Anime spoilers and MAJOR manga spoilers [Spoilers](/s "Nene was under the influence of her own charm power which led her, at that point in the series, to develop feelings for Yamada. My theory on how her power works is that it causes feelings to grow in the person to admire/love. None of Nene's crew seemed to be in love with her after she removed her power from them. Now that could just be due to the fact they're not important to the story. Ushio is the only one that "remained" after having the power lifted. And we know that many of the main cast that have the power cast on them and then removed they feel depressed. My theory is that if the person already contains feelings of love/admiration then it simply brings these feelings to the foreground and then keeps them there. We know that Ushio and Nene don't experience this feeling of depression when the power is lifted.

So with the most recent chapter of the manga we know that Nene liked Yamada before the Himekawa Memory wipe. We also know that wiped memories don't completely remove the feelings behind the memories (see: Shiraishi in the current anime arc and Himekawa where Yamada existed in her memories but with no face/name). So Yamada kisses Nene the first time and brings those feelings to the foreground and she asks him not to lift the power because she likes how it makes her feel. Yamada kisses her and she doesn't experience the depression we see in Miyamura. So at that point Nene's feelings from before the memory wipe stay there, but she (and us) don't know why they're there, but she develops feelings for Yamada for the "first time". In episode 11, post-Rika memory wipe, Nene gets kissed and remembers her feelings from before that memory wipe, and begins to act on those.")

That's a lot of stuff, but I hope it makes sense.