Arashi! retells the Testament of Sister New Devil setup: high schooler Basara Toujo gains two step-sisters overnight when his father remarries, and the new arrivals turn out to be Mio Naruse, daughter of the former Demon Lord, and her succubus attendant Maria. This alternate manga runs alongside the original rather than replacing it, giving the same premise its own emphasis: the household chaos and fan service of three strangers suddenly sharing a roof, with Basara shielding his new sisters whenever rival demons catch up with them.