Okay I forgot to mention a few merge project candidiates

I would go for a defensive unit since you have finished Soleil, which plays an offensive role. Silas fits this perfectly as he has very high Def and mediocre Atk. It honestly depends on if you’re going for minimal investment to absolute investment (low or high investment).

He also comes with a great base kit as well, Steady Stance 3 and Def Wave. It also depends on his iv, I’d go with a Def boon if you’re investing into it or an Atk boon if you’re keeping Slaying Spear and focusing on killing armours/dealing more damage. Personally, I’d go with Def.

Not sure if you like offensive units, but Shigure can be a good Galeforcer. If you have Veronica, there’s no need for Sothe as she takes the role of him.