Chapter 4 limits the party to the Celsius as Yuna prepares for her concert on the Thunder Plains. However, the party can still interact with other characters via Shinra's CommSphere network, the amount of times the player uses the network affects later events. For example, speaking to Dona on Kilika allows for Episode Complete on the Island in Chapter 5 and speaking to Isaaru in the Zanarkand Ruins ensures Episode Complete in Bevelle.