Since his time as a Special Grade student in Jujutsu Tech, you had feelings for him. You respected his loyalty to Rika, but he loved you too equally. At first, he was timid about you, but as time passed, he grew more protective of you and he grew to be the man you deserved.

If he couldn't save Rika, then he'll protect you at any cost. He'd make sure you wouldn't have the same fate as his childhood love.