The Lowly Servant is the Supreme Beast Lord

Eric is the only 7-star Beast Lord in the world, yet after his grandfather's death he chose to bury that identity and live quietly as a lowly servant. The source premise is clipped, so the story stays with that setup: a powerful beast master hiding in plain sight, carrying a past he has not yet shown the people around him. Expect a hidden-identity drama where his true strength is kept under wraps while the world remains unaware of who he really is.