I can see no reason not to get gun. I don't know any water hime with so high base multihit that they could get a penalty from high DATA on weapons (like Cybele U), just some with coulpe turns guaranted triple hit like Atlanta. So it will be less usefull then assault, but still give some buff. And it's still medium defender too so things are not so bad. Yes, hammer is better, but price is very high. If you can farm a lot ulties - get both weapons, else - get at least a gun if you can't get mlb hammer. Eydolon is garbage, just pile of orbs, Tiamat is much better. Don't forget to get 20 HE.
Kamihime ID: 4800544, wind (Hrae included)//frozen
Nutaku FKG ID: 375715584
DMM FKG ID :922767212
DMM Kamihime:4201976 - Hrae, Kirin, Cerberus