Something like Promise Cinderella

You like Hayame character??

Not sure what aspect of the story it is that you're looking for so here's a variety:

This is the most similar I can think of to Promise Cinderella https://www.mangago.me/read-manga/the_princes_cactus/

Josei/Seinen with kid in love with an adult (wholesome romance though)
https://www.mangago.me/read-manga/futari_no_renai_shoka/
https://www.mangago.me/read-manga/game_over_mizutani_fuka/
https://www.mangago.me/read-manga/mizutama_puzzle/ (this one has a college dude, not an actual kid)

They love each other but cant help but fight
https://www.mangago.me/read-manga/hana_yori_dango/
https://www.mangago.me/read-manga/the_devil_s_temptation/ (BL)
https://www.mangago.me/read-manga/namaikizakari/

yes, she was fun and unpredictable. But she also didn't lead anyone on as I thought could happen, even when she was confused or hesitant, she was an honorable person. Since I can't take it seriously I am not judging her by rl standards to be fair.

Thanks so much, I'll take a look.