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+C: Sword and Cornett
07-Ghost
legend of the sun knight (but I suggest you read the seven books in the series...really funny and entertaining at the same time.)
Adekan (gorgeous art and wonderful story)
Asterisk and Jinjuu Horetsuden by the same author (idk if I spelled that right)
Banana Fish
Black Haze (it's in full clot to boot)
Black Joke
Demon Diary ( demon Lord and his caretaker ;) )
di[e]ce (friends but I love this one too)
Gin no Yuusha
Hakkenden - Touhou Hakken Ibun(it hasn't updated in a while but you can always watch the anim. It has really beautiful art)
Hayabusa - Sanada Dengekichou and Tokaidou Hisame by the same author
Ilegenes - Kokuyou no Kisekiand its sequel (not the master slave type of relationship but the sconce or is very good and the art is gorgeous)
K - Memory of Red(read the associated manga too and even better watch the two seasons...I'm in love with this one)
Kami-sama no Iutoori Ni(it's horror an you might not like the art at the beginning it it's good, if you live survival games that is)
Kyou kara Ma no Tsuku Jiyuugyou!
Lost Seven
Lucky Dog 1 Blast
Nabari no Ou (either the anime or manga will do but beware of tragedy)
Noblesse(I love the Little group of knights they've made ;) )
Nurarihyon no Mago
Owari no Seraph
Pandora Hearts (it's long but I love Oz's and his caretakers relationship)
Saihate no AoAction
Saiyuki
Saiyuki Reload
Samurai Drive
Sennen Meikyuu no Nana OujI (totally recommended, all of them have a similar relationship with the main chara)
Shichifuku Mafia (familiars)
Sougiya Riddle (contract type of relationship)
Tales of Zestiria - Michibiki no Koku
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1001 (updates are like really slow)
Amatsuki
Data (sadly it's not competently scanlated)
Pirates and the mermaid
Shunkan lyle (hadn't updated in ages)
Teikoku kyoudai
Ryle to yari
Number (I love this one)
Betrayal knows my name (again translations are slow so watch the anime in the mean time :) )
Waltz...if you like blood and gore
Code: leviathan
There are more but I'm too lazy to search and remember....
Enjoy
I am looking for manga like shirogane no ou. The story need not be exactly same but i love the relationship of the main characters. Please recommend if u knw such mangas :)