Using his solar power, Duke creates a barrier out of fire; when enemies come in contact with it, they are set ablaze. This force field can reach temperatures hotter than the sun and can be used offensively to blitz through hordes of enemies; burning them in the process.
Duke has the power of heliokinesis, solar manipulation, giving him the potential to use this technique.
Users must have powers that, in some way, relate to fire; and they must have enough control over it to change its shape and size. Creating a defensive wall of some kind.
Enough force can break through the barrier.
Unless the character in question is somehow fireproof, coming into contact with the barrier will result in them getting burned; regardless if they're friend or foe.