Aias

Aias is a Great Knight that appears in chapter 13 of Eirika route. This is the Chapter you can recruit Cormag in by speaking to him with Eirika. They're are two Ballista with two enemies that can get on it before you do. Also in this chapter, you can recruit Amelia in this chapter with Franz or Eirika if you didn't in Chapter 11.

When you kill him, you can get a Knight Crest. It seems he is a friend of Caellach and worked with him in the army. Near the end of the Chapter which is a survive for a amount of turns, Councilman Pablo arrives with troops. He's holding a Divine and he's a Sage.