Well, I'm looking for a manga that's got a theme involving 'taming a beast'. The best example I can think of currently is in Kemono no Souja (I highly recommend watching the anime), Erin forms a bond with Lilan, an Ohju/Beast Lord from the wild. Lilan is a type of Beast Lord thought to be untameable to a sense since Ohjus raised by humans are completely different. Oops a bit off topic, but this kind of relationship is what I'm looking for in a manga
The 'beast' has to be an actual beast although a beast that can transform into a human would be interesting as well. Extra points if there's romance

Errr... technically, she tames a "beast" (okay, it's a lion, but still... it's not like she's controlling a pet cat or something)... it's a pretty interesting concept: Barairo My Honey. (The focus is romance.)

Alright, I'm not sure if these even count but:
Natsume Yuujinchou - main character has a spirit cat
Demon Seiten - there are different demons (beasts that can transform into humans) and their respective masters
Hoshi no Samidare - more of a comedic relationship between the animals and their knights

Ushio and tora

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maybe Beast Master ? I like that manga

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moje oblíbená (my favorite):

Seconding Beast Master

Her Majesty's Dog

@hobbitelf518 Yeah it is a very interesting concept. I've read Barairo my Honey and unfortunately i couldn't bring myself to read past the 4th chapter. Not that it's terrible it's just...bland i guess?
@skat Thanks for the suggestions ! Demon Seiten sounds interesting
@Avian3 The art's a bit hard to swallow for me but I'll try it out
@Elianir and fbunawan I've already read those mangas but yet to finish them, thanks though.