Surprisingly easy for me, I beat it on first try with my main team. 5* Nino, Sharena, Ninian and Jaffar. All have some SI.
On first turn I position my units. Then Nino kills the spear guy, Jaffar reposition her, Ninian dances for Nino and she draw back Jaffar. No one can touch me. Enemies approach. Then Sharena attacks Xander and blocks the other red guy. Ninian dances for her and kills Xander. Jaffar kills the green mage and Ninion draw him back. In last turn Sharena finishes off the red guy and Jaffar does the same with the healer.