I would unironically go with Nikaido. Besides being a master of fighting groups and using concealed weapons, he commands a very effective group of assassins that would probably grant the most security.

Raian, as strong as he is, is way too unpredictable. I wouldn’t rely on him to protect me from an entire group that would probably use more strategy than Raian’s willing to overcome.

Muteba is probably even better than Nikaido at fighting in groups, but I think he’s a one man army. While he would be effective by himself, he doesn’t have a group backing him up like Nikaido. If we had to pick just one fighter without any backup I’d pick Muteba.

Rei and Kuroki are mostly just good at killing a few people at most and then leaving. I wouldn’t rely on either of them against a large group. Kuroki is probably the worst option here because we don’t know how effective he is against large groups. We saw that he and Rihito took out a bunch of guardians, but that was all offscreen. For all we know Sawada mighta shown up and beat them all for them.