A few minutes after Klaus returned to the surface, the black panther killed Arwan by clawing his heart out.
It was brutal, but he got the job done, which was the most important thing.
Though it took some time before he killed Arwan, in the end, he managed to bring down a major threat.
The main reason he wasted that much time before killing Arwan was due to the fact that he wanted to test his strength after the bloodline awakening.
Having the blood of a goddess flowing through his veins made him feel invincible. So he went against a level 4 Ascension stage warrior to test his strength, and he prevailed, sustaining only minor injuries.
He turned and looked at the large, chaotic battle still raging on, and a smile formed on his lips.
As he looked at the teams from the Bast Race handling their own, he felt a surge of pride.
Of course, he also saw what Klaus's side of the team was doing, and the only logical explanation whatsoever was to just ask later.