If you don't know which stunner to pull for...
There's a neat little website you might know of called zfae which is mostly just for people to upload their builds, but it recently got a calculator feature.
There's been a lot of questions here lately about which stunner would be better for him so I decided to hop on and see what it says. Now take this with a grain of salt cause I dont think it takes into account ALL that goes into playing Harumasa (like quiver generation for example) but the results are as follows:
Norma and Roxy seem to be around the same level with Dialyn pulling ahead (to the surprise of absolutely nobody) and the score goes up to 56K if you put Harumasa on Puffer instead.
Also if you have Trigger M2W1 or higher she's actually better for him than both Roxy and Norma
AGAIN this is not in any way a definitive answer but I hope it was at least a tiny bit helpful