Keep in mind that Red Demon God makes a point out of Kiri being the only person to ever cause Kouma pain (and he does it twice with the same spot). I would definitely say it's a Chekov's gun of things being different here.
That said, Akiha or people with powers as ridiculous might be able to mess him up, unless he gets MR out of his blood, since Plundering is a low level effect that's really powerful when it works.
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Maybe it's the time Arach arrived?