Obtain: Extra Stage 1, "Dark Show Opening", unlock by passing the "Attend the Dark Hero Live Show."
The Dark Hero acts as a defensive variant of the Steward; with higher aptitudes in DEF and RES, while also sporting slightly higher base stats in ATK and SPD.
Unlike the Steward, whose Evilities are completely reliant on being next to Valvatorez, the Dark Hero's are focused on reducing damage. This makes him absolutely invaluable in the Item and Chara Worlds, while also making him an excellent damage-soaker.
The Dark Hero learns all Fist skills as well as Sword skills up to the 4th Tier. In Disgaea 4: A Promise Revisited, he can also learn the Tier 9 Fist skill Libra Pasio, which was previously locked to the Necromancer DLC class.