Avenger Of Mystical Eyes - Blood Parasite summary:

"Do you want to be my family?" Archive, the devil race's weakest, was saved by the Demon Lord right before death overtook him. Unable to have children and capable of harming anything that approaches him, archive is the only Demon King's "family" that makes his life happy. However, demons and humans hate each other, and they are fighting wars for the sake of each other's peace. Eight heroes lure the Demon King with promises of peace to defeat her. In front of Archive, the weakened Demon Lord fell into the trap and ended up being abused. Archive goes to help, but as the weakest demon, he has no way to fight back and ends up being decapitated, and the Demon King ends up being sealed. If he had the power to protect the Demon King, Archive would use a bit of his strength to cast a certain spell on one of the eight heroes, Lieselotte. By using this magic, Archive managed to take over Lieselotte's fetus which was already pregnant. Reborn from the weakest demon into the son of a hero, Archive has a “demon eye” that appears suddenly. Petrification, Charm, Fear, Clairvoyance, and many more, Archive obtained the strongest demon eye that can use any kind of power. Archive vows revenge on the heroes, even if it was his own mother who gave birth to him, or the lover who loved him when he was a teenager. “Wait, you heroes–I will kill you and definitely take back the Demon King!”