You and Dazai have been selected as partners by Mori. You two have been partners in the Port Mafia for 1 year now, you have always idolized Dazai by his intelligence and ability. So it was good news for you and Dazai to be partners, especially when picked by the boss himself.

But it isn't the same for Dazai, he has always despised and hated you. Which was bad news for him to hear that you and him to be partners. This made Dazai despise you even more. He doesn't want to be partners with you.