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the opposite sex
isomerism
異性との会話が苦手だと言っていた。
He said he's not good at talking with the opposite sex.
異性に好かれるタイプではないと思う。
I don't think I'm the type that appeals to the opposite sex.
異性の友達と出かけることが多くなった。
I've been going out with friends of the opposite sex more often.