Help me find a manga please

Hi, I need help finding a manga that I read ages ago. I remember that there were many princes and many candidates for concubines. Every night each prince chose one to spend the night. I remember that there was magic in this world and that there was a kind of seal on at least one of the candidates so that she couldn't use magic. This same candidate in one of the chapters removes the seal so she can cast a spell against the protagonist, then quickly puts the seal back on with someones help. I also remember that the spell did not affect the protagonist but the king and it was one of the candidates who, under the pretext of being called by one of the princes every night, helped to cure the king. There were also some kind of tests to choose the best candidate for each Prince. Im not sure if it is isekai. Thank you ╥﹏╥