1
brother-in-law (spouse's younger brother or younger sister's husband)
まさか惚れたんですか。認めん、認めんぞ。あの男を義弟になるなんて、僕は絶対いやです！
You haven't fallen in love, have you!? I won't have it! Having that man become my brother-in-law; I absolutely hate that!
2
younger stepbrother