Silly ideas.

It's about the same character so I am not making 2 chapters.

Idea 1:

Random person walks through a con while cosplaying Regulus from Re:Zero, only to be blinded at some point and wake up as the actual Regulus right before Petelgeuse takes in the Witch Factor of Sloth.

Honestly, not much thought behind this. Not really interesting or original, but I think it would be interesting to see the degradation of the main character since they don't have enough greed in them like Regulus.

Idea 2:

As Subaru gets in the world of Re:Zero, Regulus also gains the return by death ability.

Excepttttttttttttt.

His ability triggers once he kills someone or lets someone be killed.

Nothing much to explain here.

You could connect it with Subaru's ability as like both of them go back at the checkpoint once Subaru dies or Regulus kills someone.

Or make the abilities not connect each other. You choose.

You could also try to explain why Satella gave Regulus such a thing (if you even decide to make her the reason why), but I honestly didn't think that far.