Agni & Rudra are a pair of living, twin demon swords sealed away by Sparda himself in Temen-ni-gru. They are the boss of Mission 5 in Devil May Cry 3: Dante's Awakening. After their defeat, they're playable as weapons to Dante.
Devil May Cry 3: Dante's Awankening
Dante comes across the brothers in the Firestorm Chamber. They are at first cordial to Dante, discussing how to be "gracious hosts", but when he demands to be let through their gate, they attack. After Dante defeats them, they ask to be taken with him as Devil Arms, and Dante agrees on the condition that they remain quiet...which they repeatedly fail to uphold, for which they are punished.
Both swords possess the same design as a uniquely shaped scimitar with jagged edges with a color scheme befitting for their respective element in which they manipulate. The blades are serrated with the segments appearing to interlock like a Celtic knot. The ends of both are slightly jagged but not pointed as a normal blade would be. The pommels form the talking "heads", and the guards of both are round and plain. While Agni sports a red theme, Rudra sports the blue theme.
Compared to most other demons which are belligerent towards human beings just by their nature, Agni and Rudra desire to be a gracious host to anyone who enters their room, provided they don't want to go through the door they guard. Agni has some knowledge of human customs and gestures, as Rudra doesn't know what a "sigh" is, though Agni doesn't have the chance to explain. Overall they generally possess affable demeanors (especially in comparison to other demons), despite failing to uphold Dante's stipulation that they don't talk on the adventure.