Karasu is the commander of the North Army in the Revolutionary Army. He ate the Susu Susu no Mi, a Logia-type Devil Fruit that allows him to create, control, and transform his body into soot(fine black particles consisting mainly of carbon and created by combustion) at will.
He commonly uses this power to mold his soot into the shape of a flock of crows, as well as breaking up his elemental body into crows.
With his Karasu Renkon attack Karasu breaks his body apart into a murder of crows to assail a specific opponent, by having the crows rapidly fly at and peck said opponent in rapid succession.
His soot crows are able to fly at high speed and can relay information to his allies either by him speaking through them or delivering newspapers. The crows can also be used in combat, able to disarm enemies en masse by snatching away their weapons or by attack his opponents directly. Additionally, each crow is capable of carrying an average-sized person on its back.
Karasu can use his soot in other ways as well, such as building it into constructs. With his Obelisusu attack Karasu moves swiftly past a potential multitude of enemies while transformed into soot, leaving traces of the substance between their feet. He then causes the residual soot to shoot upwards in the shape of thin, obelisk-like spikes, causing piercing damage to said enemies while sending them flying.
Karasu can fly by transforming his body into soot, even without his crow wings.