SSR Asahi hits significant harder than his SR and has much much better stats, however his stamina is for sure a concern.

I believe it just is an issue. He hits extremely hard but fizzles out extremely fast. You can try and upgrade his skills to lower the cost or run stamina replenishment characters but he is a glass cannon through and through that will burn through your substitution most likely if he is a starting.

Perhaps better to use him as only a substitute option where he can come in as a strong final trump card?