As police uncover a far-right group behind a series of grisly murders sweeping Japan, a police officer and former ultra nationalist seeking redemption must go undercover to prevent his younger brother from going down the same wrong path.

There’s something to this, consider the following:
To keep from following two goals (police – group behind bars | far-right guy – rescue mission), two unconnected protags but one brother, I produced this.

Example:
“A former ultra-nationalist must rejoin a far-right group behind a series of grisly murders sweeping Japan in order to rescue his wayward younger brother”

You can up the stakes by adding a “before” element at the end e.g., before the police catch up to him.

Hope you find this constructive, make this yours, keep going!