 If you liked
Risou no Himo Seikatsu
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 ...then you might like
Genjitsu Shugi Yuusha no Oukoku Saikenki
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These are both Manga
Both are similar in that in both a male are summoned to an otherworldly country. Both take on political work. However, in Risou he is not a king but a prince consort in a currently monogamous marriage with the queen of that country. In Genjitsu the main protaganist becomes the king and there seems to be plans early on to have multiple wives. Both are good (in my opinion of what I have read), with more focus on the marriage part in Risou.