Laguna is an obvious one for me. His story as a soldier was always interesting and his travels would be a good story if not an interesting game.

The journey of Lulu's original pilgrimage would be interesting if a little bit anticlimactic. Auron and Jecht's pilgrimage with Braska would be awesome.

Fratley's journey to rediscover his memory would be awesome too. Even just more on Fratley and Freya would be nice. Quina and Amarant are also underdeveloped.

A lot of the cast in VI could do with more. Setzer is a favourite of mine and his gambling could lead to all sorts of shenanigans.