Maki is a moron. Maki has sex with a girl and copies her skill. Then she kisses Kenta, and transfers it to him. Maki could then copy back that same skill from Kenta, or the girl she got it from originally, and just keep it. Then both Kenta and Maki would have the same skill. There is no reason for Maki to stay weak, other than as an excuse for Kenta to constantly rescue her.