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Koro~sensei created a topic of One-Way Romance

I’m a bit confused with the side story. So far I’m on side 4 but if the brothers have a rule that prevents the from harming each and the ppl around them then why can the brother with white hair just take back the mc? He was technically his persin first and his brother was the one who kidnapped the mc so wouldn’t the brother have already missed up the agreement?