Sirius should be referred to as His Highness since he is only a Prince, Not 'Your Majesty'.
I think Ombra's name is supposed to be spelled Umbra. Both words mean the same 'Darkness/Shadow' - But Umbra spelled with an U is for ''Human'' Naming. while Ombra is for objectively naming.... sorry, I can't explain better than that. ╥﹏╥
Otherwise the story was good, I did enjoy it, I consider buying the official english manga. And RIP Muuto - what a beautiful way you left the world.
uhm author maybe you should look up feet sizes, cause it literally looks like he is kissing a 4 years old foot ( ̄∇ ̄")