Not only was another girl introduced, she is in love with Eiji too. This makes 4 girls who love Eiji now? And Nanako was supposed to be the popular one, but le only had one other guy after her whom she rejected immediately.
1. Koto-nee
2. Nanako
3. Komachi
4. Iori
It was funny how the painting girl at first was teased as a rival but was immediately shown as a false flag, but now the author has introduced multiple rivals.
That being said, I don't really mind. This is a comedy with romance in it, not a romance first manga, and there is no need to argue about a winner, since Eiji X Nanako is exceedingly obvious. They both love each other, have been in love since before the story even began, are the two main characters of this. And the story is refreshing in how it doesn't go down any generic love rival trope, Nanako got along great with Koto, she and Komachi are close friends, she likes Iori too so far. And no one is trying stupid shit to steal anyone away from someone.