Bune was tasked to keep watch about an Overlord beast's movement. Although it was a suicidal task, he accepted it gladly. Bune was confident to survive from the Overlord beast's attack, simply because his flame was colored violet, more potent compared to red and blue flame. Only White and Black flame could overpowered it.
Furthermore, Bune has the bloodline of his foreparent, an Ancient rank monster. Bune was talented among the violet infernals, too. With all that reason, even he deluded himself that the Overlord beast should have feared him.
Ironically, he avoided fighting even the Corrupted rank under Herforao, simply not wanting to alarm the latter, even though Herforo was already aware of Bune's presence. Since Bune did not attack, Herforao let him be. Bune just badly wanted to deny he was terrified of Herforao.