During the prologue section of Suikoden Tactics, we see Sir Walter joining Edgar and Brandeau on their expedition against Steele. Walter takes Andarc and Yohn along with him, and orders Seneca to stay behind and take care of Kyrill, entrusting his son to her care in the event that something terrible happens to Walter. And what happens 3 seconds later? Seneca loses sight of Kyrill.
Kyrill sneaks on board the ship and in the battle with Steele, he witnesses his father transforming into a monster that tries to kill him, and Andarc slays Walter to rescue Kyrill.
From that moment on, Kyrill is compromised - he can't bring himself to kill any fish monsters after the trauma of seeing his dad turn into one. And Andarc is consumed with guilt, constantly apologizing to Kyrill and re-swearing to devote his life to protecting Kyrill and make up for what he did.
And Seneca's attitude? Chill out guys! What's with all the long faces? Stop being so down all the time.
Girl, if you'd kept a better eye on Kyrill when you were on that tiny little island inhabited with drunken rowdy pirates, he wouldn't have been on that ship in the first place.