Genryuu Butouten: Origin

Jin is a carefree high school student with powerful abilities that only activate once a month. His friend Fusano, who is physically attractive and takes combat seriously, contrasts with his laid-back attitude. When Jin is confronted by aggressors on a day when his powers are inactive, it is revealed they were sent by his estranged brother, Soichiro, who wants something Jin has. After Soichiro attacks Fusano, the two brothers become openly hostile.