Because the way he sees it the imperials are hounding him due to the stupidity of a single man challenging his whole damn group to a duel. As in for a stupid reason - and as he sees it for a 'dishonourable' reason. Toki may fight underhandedly, but he has his own sort of code of honour after all, the fight may not have been 'fair' for the captain, but the fellow shouldn't have challenged all of them on the spot.

Besides, police work pays better than banditry and might be better on his health. Getting to let the air out of imperials - who deserve it - is a sort of a nice bonus to that.

Also since he has now worked under few samurai Toki has come to the conclusion that it is better to have someone to actually direct their guns to the 'correct' direction rather than leaving himself and his crew to their own devices.