Oh man, I am so happy that Morgan is the secret keychain in this volume since it technically means that I have both of my kids.
See, in my game, I married Tharja, so my two daughters are Noire and Morgan. The secret keychain here is the MALE Morgan which makes sense given that Volume 1 had the FEMALE Avatar/My Unit/Robin.
Volume 3 has the MALE Avatar/Robin, so I’m hazarding a guess that the secret keyrings for Vol 3 and 4 are Tharja and FEMALE Morgan respectively.