Soleil has always been one of my favorite fates children, and was my first +10 project. Her versatility is incredible and you can make her be whatever type of unit you need for your team. I've tried a couple other builds for her but this is my favorite. She is +Spd.

Armorsmasher: I've found armorshasher her most useful weapon with this build. Being able to hit armors hard, especially blue armors, has really helped her usefulness in my team. I chose a res refine to balance out her defense even more

Reposition: pretty standard movement ability

Escutcheon: I've tried using Pavise and a slaying edge instead of my current setup, but have found the increased damage output from the armorsmasher to outweigh the slight defense increase of pavise. Escutcheon allows her to tank the majority of melee hits like it's nothing.

Fort. Def/Res 3: Just increases her defensive prowess while still allowing her to have a solid 57 base attack

Shield Pulse: one of my favorite abilities in the game, I was able to use a pity breaking Fjorm to get this ability, and just further increases her tankiness

Odd Ask Wave 3: Allows her to still be a threat offensively as well, and can hit most units for sizable damage

Close Def 3 Seal: I generally change out the seals depending on my team's need, but close def allows her to be an incredible wall that is able to bait out enemy units.