Sorry, I thought there were more than 20 chapters. But yes, it was Kimi Koi Limit. Thank you both.
Actually there is another manga I can‘t find anymore. It‘s about a superficial girl who wants to become an idol or compete in a beauty pageant or win some kind of popularity contest or something like that (can‘t remember). She gets saved from a pervert by some delinquent chick on a train and at the end they become a couple and the superficial girl stops giving a shit about beauty pageants etc. I remember the delinquent girl wearing a face mask most of the time.
It‘s a vague description, but does somebody know it?