http://www.mangago.me/read-manga/gosan_no_heart/
Unexpectedly carnivorous..., like this?
http://www.mangago.me/read-manga/koi_wa_itsumo_arashi_no_youni/
Aagh. I've already read Gosan! But thanks!
As for the second one, kind of. It's more like the seemingly innocent seme who gets really mischievous and naughty in bed.
umm promiscuous as in playboy uke? i don't have them tho but if you like i had a collection of uke who loved sex but most are pretty much committed to their partner when they started going out. http://www.mangago.me/people/tag/49344/lewd+uke/
also, the seme that you described had me remember these guys
a traditional and straighlaced japanese man but transforms into an insatiable wolf when worked up http://www.mangago.me/read-manga/memory_of_the_future/
a gently cry-baby younger seme but gets aggressive and hunky in bed http://www.mangago.me/read-manga/ichiban_chikaku_de_koi_o_suru/
'notice-me-sempai' type http://www.mangago.me/read-manga/sweet_chapel/mh/c001/
Looking for yaois with promiscuous ukes who fall hard for their seme! The semes are preferably the more indifferent type who only get wild in bed. ლ(´ڡ`ლ)
Ooh, and I'd love other yaois with unexpectedly carnivorous semes! Like:
http://www.mangago.me/read-manga/koisuru_barairo_tenchou/
(≧∀≦)