Do I Have to Kill Claude?

The Imperial forces engage Claude in battle, and emerge victorious; Nader is driven off, Derdriu is brought under Imperial control, and Claude is spared or executed at the player's discretion. If Claude is spared, he approaches Byleth and Edelgard to explain he is leaving Fódlan.

Can you recruit Claude Blue Lions?

You can't recruit the other house leaders, Claude, Dimitri, and Edelgard if you don't pick their house. Characters like Dedue and Hubert, who are both incredibly loyal to Dimitri and Edelgard, are also unobtainable if you don't choose their respective house.

Do you have to kill the students Fire Emblem?

3 You Can Recruit Certain Students After The Time Skip

Due to story scenarios, the characters Lysithea, Lorenz, and Ashe can be recruited even if you had not gained supports or had no intention of getting them. However, they must be defeated by Byleth in battle, since any other unit will result in them dying.