Bodyguards are fighters that protect the demon bosses. All demons have five bodyguards. Before one can actually battle the demon, they have to beat their five bodyguards. Bodyguards have their own speaking roles (except Shin).
The first three of Wasp's "bodyguards" are the members of New Blood, a group consisting of crew members that have rebelled against her. Bosun is the only one loyal to her, as all the others are part of New Blood or disloyal.
Widow's "bodyguards" are mainly composed of men that have been charmed. The only exception is Puma, a woman who serves Widow to help her achieve her ambitions. Most bodyguards attack Shadow in an attempt to eliminate the competition, because they are mistaken in the belief that Shadow desires Widow as they do; He merely wants to obtain her Demon Seal, and has no interest in her whatsoever. After being defeated by Shadow they are released from Widow's spell.
Titan's bodyguards are the evil counterparts of Shadow from another dimension. In that dimension he was not strong enough to resist the pull of Shadow Energy and ended up getting corrupted by it. After defeating the Demons, instead of moving on to the next province, he ended up staying and taking over their syndicate.