Remg
from what I remember ... Rias has a weak body (she doesn't exercise, she cares more about magic) and has little control of its destructive power ... So, to make her stronger in no time ... I imagine I could buy the meditation technique of "Yue Yan" from long live sumung ... where she trains while she sleeps (so that Rias can get stronger while she sleeps ... and improve control of her destructive power ... since Rias is a bit lazy ...) not to mention that at the moment it has not been mentioned that Rias spends long hours training.
hakai, but she will be very op, but you can make some restrictions because the hakai can only be used by the gods, it is if she uses it a lot can ... And the fact that she can use the hakai is because she is already possesses the energy of destruction even if they are not at the same level. she can still use.
Hmmm. I just don't like the fact that Yuechan wanted to be cuckold. Seriously, Bruh? "Please pick more girls, etc. etc." Yuechan said that many times. Like seriously? She really had NTR fetishes. Bruh? Just bruh moment for me. Bruh? (didn't read ATG. don't know her personality. but bruh? she really was excited getting cuckold.)
I could only think of 2 route first either make rais transform chaos into their original element ( 7 nature element) than she need to control all elements to master her Chaos form second option turn rias in Megumin 2.0 give rais Op Nuke semi Hakai skill where she turn all her energy into little semi Hakai attack skill and fire it just like Megumin. than send rias to universe 6 to learn Hakai from vados and save universe 6 and join tournament of power