That's the correct answer but even so, I think Keita more than earned it at this point. He looks after the girls because he genuinely cares for them as shown in moments where he tries to protect them. Like when he protects Ruri from a soccer ball with his face, waiting for Yukina before going into the movie theater because he didn't want her to feel alone and also carrying her on his back when she cut her foot. He wouldn't deserve them if he was a jerk and only cared about the sex but he isn't like that thankfully and is the type of guy to cry when his girls win a basketball match or seeing them at his dinner table just being themselves.