In the chapter it’s shown that the Gorosei’s bodies are formed out of black lightening when summoned. If you check the chapter where Saturn recovers from Kuma’s attack his body also seems to be reforming out of black lightening.
IMU is using some new Haki skill we have not seen before to make his Haki visible and solid shaping it into the form of the 5 Elders. Damage doesn’t work on them since they are just Haki. The only way to defeat them is to use Haki >= IMU’s.
Though when I say we haven’t seen it before it’s possible we saw it with Zoro’s Asura. Kaidou seems to hint at Asura being Haki based and it appears to become tangible at certain points too.
IMU is using some new Haki skill we have not seen before to make his Haki visible and solid shaping it into the form of the 5 Elders. Damage doesn’t work on them since they are just Haki. The only way to defeat them is to use Haki >= IMU’s.
Though when I say we haven’t seen it before it’s possible we saw it with Zoro’s Asura. Kaidou seems to hint at Asura being Haki based and it appears to become tangible at certain points too.