Baku is the main antagonist of You Are Umasou. He is the possible biological father of Heart.
By appearance, he looks similar to Heart but is larger and has a darker shade of blue. He has two scars over his missing eye which he lost after a battle with Giganotosaurus.
He is very commanding over his fellow T.rexes and does not tolerate anyone of his kind betraying him and is very brutal when it comes to fighting.
Despite his seemingly cold nature, he decided to spare Heart's adoptive family since they raised him. He is not bothered that he lost the one egg that may have been Heart.