[YoshL]

if you had a skuld or beach urd that you can get viable, they work well for a 4th slot (big heart generators with potential spike board actives, as well as water enhances and tpa)
but for that, andromeda i think is probably your best 4th slot because the tpa over gabriel. you're never going to really be doing rows, and the little bit of extra dmg is nice.

hermes breaks hearts and you don't want that
lakshmi doesn't really have a useful active, you just want hearts at all time. if you have a heart cross, you're alive is the general rule

5th slot prolly would be flex depending on what dungeon you're going into. orochi's quad dongers are superb at shitting out damage, and delay is useful. if you're getting bound, definitely go isis, since she's also good w/ a couple extra water enhances (since you have 16 with 3 sumires + friend leader sumire)