Bottom Teacher with Top Student

I hope you're looking for legal ones

https://www.mangago.zone/read-manga/dou_imo_nara_nai/
https://www.mangago.zone/read-manga/pink_to_mameshiba/
https://www.mangago.zone/read-manga/katakoi_alliance/
https://www.mangago.zone/read-manga/kudou_sensei_no_majestic_days/
https://www.mangago.zone/read-manga/ayashi_no_hakoniwa_ni_ukabu_tsuki/
https://www.mangago.zone/read-manga/sweet_beast_suji/
https://www.mangago.zone/read-manga/hatsujou/
https://www.mangago.zone/read-manga/i_ll_educate_you_on_everything/
https://www.mangago.zone/read-manga/ochikobore_alpha_to_elite_omega/
https://www.mangago.zone/read-manga/sensei_zenbu_dasasete_kudasai/
https://www.mangago.zone/read-manga/haru_kakete_uguisu/

Teacher and former student re encounter
https://www.mangago.zone/read-manga/come_to_hand/
https://www.mangago.zone/read-manga/hatsukoi_no_tonari/