Man-nen wo Ikiru Heiwashugi Vampire, Itsunomanika Seikai Saikyou ni: Ore ga Maou-gun Shitennou de Aratana Shiso? Dare to Machigatten no?

Alto, a vampire who describes himself as "slightly weaker than average," receives a letter addressed to "Lord Alto: Ancient Vampire and One of the Demon King's Four Heavenly Kings." Suspecting a case of mistaken identity, he nonetheless accompanies the beautiful vampire girl who came to fetch him to the Demon King's executive meeting. ...Wait, am I the strongest of the Four Heavenly Kings? As tales of his legendary exploits, feats he has no memory of, are recounted, the group decides on a new objective: slaying the Hero! The only problem? The Hero is someone he actually knows...?! For some reason, he finds himself feared and respected, getting swept up in a massive crisis. Just then, a legendary dragon awakens, plunging the world into peril! ...I mean, I have no idea what's going on, though. Thanks to a massive misunderstanding, the curtain rises on a fantasy comedy about an overpowered pacifist vampire! ...No, wait. Aren't you mistaking me for someone else? (Source: MANGA MILLION)