From Ferrus

"" is an Series: in. As its name suggests, it is a ST: from ST:.

Location and Uses
"ST:" can be collected from any ST: after ST: has delivered ST: to ST:, dousing the NaN Lava Geysers that blocked access to the village's homes. ST: writes that he is out photographing NaN Armored Trains and suggests that ST: pay him a visit. The ST: includes a picture of a location in the ST:. It reads,

The location in the photo can be deduced as the southwest area of the NaN Spirit Tracks (Object)s outside of the ST:. ST: can drive the ST: to this location and meet with ST:, who asks the young engineer if he could be taken to meet his hero and all-time favorite engineer, ST:. ST: can choose to drive ST: to ST: to meet ST:, for which he will be rewarded with ST:.