[ He's not obligated, but Akutagawa still doesn't quite understand this man's motives. Just because he's in the position to fend of ayakashi, he will do so. But where's the goal? What does he gain? More experience, more insight?

He agrees that it would be a waste of his knowledge and skill if he doesn't utilize it when the time arrives. However, because he does have this experience, his knowledge is invaluable. He could educate others and solidify his place in the heavens as an asset. Yet, this man doesn't seem hungry for power and influence, which Akutagawa finds a bit disappointing.

Despite Shun denying that his actions are altruistic, simply wanting to prevent someone from suffering from an ayakashi sounds pretty generous to him.]

I understand that it's a god and shinki's duty to eliminate ayakashi. If you're not being chivalrous, then what are you trying to achieve?