It's a bl quick transmigration novel. The merman arc i remember was set in interstellar era where merfolks are mostly (or only) able to give birth and so i think they were used for marriage but not quite so..... I think it was more of an agency where merfolk are breed then given or sold for marrage?? Not sure buuuuuut The marshal or general idk got himself a merman and his subordinate also got a merman which is the mc and then the marshal wanted to switch merman partner with his subordinate because of course he likes the mc more lol that's all i remember uwu If anyone knows, have read and remember the title please tell QAQ
https://www.novelupdates.com/series/its-actually-not-easy-wanting-to-be-a-supporting-male-lead/ Arc 7
It's this one, thank you QAQ idk why i skipped it everytime i'm searching QAQ Thank you all for answering~