Kostas (Japanese: コスタス Kostas) is a character appearing in Fire Emblem: Three Houses. He is the leader of a pack of bandits, hired by the Flame Emperor.

At the beginning of Three Houses, Kostas ambushes Edelgard, Dimitri, and Claude at dawn, intent on killing them. Jeralt and his child Byleth arrive just in time to aid them in defeating Kostas and his band of thieves. After the battle, Kostas attempts to kill Edelgard, but Byleth protects her from the attack, putting them on the verge of death. Just before the attack can connect, a mysterious power allows Byleth to rewind time to the moment before the attack, allowing Byleth to counter Kostas' blow and save Edelgard. Kostas and his remaining henchmen retreat when the Knights of Seiros arrive to apprehend them.

Later at the Red Canyon ruins, Kostas objects to the deal being given to him by his employer, the Flame Emperor, since having to battle the Knights of Seros was not part of it. The Emperor calls Kostas worthless for worrying about the Knights of Seiros and chides him for underestimating them and departs to find Kostas' replacements before he can argue further.

Kostas battles Byleth and their class when they reach the canyon under Rhea's orders and is slain.

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