[Maybe, on some level, Akihiko recognizes Serph's demon form. Remembers seeing it from before, and how they'd established a sort of truce... Or maybe as a raiju, he's just much more interested in different meat, and sees that water demon as too much trouble to fight.

Contrast with the bear he keeps trading jolts of lightning with. Akihiko is little more than an azure, snarling beast at this point-

...But he can still distinguish light. And understand screams. And when he leaps backwards, it's in part to keep himself between the bear and a glowing, slightly familiar face.]