/cgl/ - Cosplay & EGL

>>9621357
>>9621360

It's a raglan sleeve, but one that has been adapted for a more open, square neckline, and then widened to be puffy sleeves. Pic sort of related, the blue line shows how cutting the normal rounded neckline into a square shape will result in the kind of sleeve shape you see in your OnS pattern.

I don't have advice for actually lengthening it, but if you can find tutorials for lengthening raglan sleeves you can now compare the shape back to your OnS sleeve and see how to lengthen it.