Frog was settled in the fight against Magus. Therefore, Frog has lost the reason for having to fight. And, Frog is still remaining regret. It is to have killed Cyrus. Frog fight for the world from now on, must be settled in the past with Cyrus. Cyrus, now become a ghost that are wandering in the "Northern Ruins" of the "Choras Village".
600 A.D. Northern Ruins
First of all, because everywhere in the "Northern Ruins" in 600 A.D. is damaged, it can not enter the interior to do a repair. Also, at this point, when going to the "Northern Ruins" in 1000 A.D., the ghosts of Cyrus, which could not sleep peacefully for 400 years, will attack. It can not be managed this ghost.
600 A.D. Choras Village
Crono is go to the carpenter's house in the Choras Village, it is possible to know that the carpenter is in the Cafe.