>>718181502
Towa is properly introduced in Trails of Cold Steel. Her games are primarily the Cold Steel quadrilogy and Reverie (which is literally Cold Steel 5).

Do keep in mind that all of the Trails games are connected and it IS one long overarching story so you technically should start at the beginning with Trails in the Sky. But Cold Steel 1 is also intended as another jumping-in point and frankly I started there too so I'm not gonna tell people they can't do the same.

Towa appears right from the start of Cold Steel's prologue chapter, you can't miss her!