If a crit does happen, it's more likely for Ryoma.
However, Xander does have skills giving him additional damage dealing. He does get additional 3 damage to his attacks always. Plus additional 2 at full health, and takes 2 less damage, when initially at full health. So, Xander can do extra 5 damage on initiation. Another thing is, Xander has more movement than Ryoma, Xander having 8, Ryoma has 6. So, Xander could move back, forcing Ryoma to move forward, then Xander initiates on his turn.