Friendship Gauge

From The World Ends With You - Wiki on Neoseeker

The Friendship Gauge shows how close you are to a certain shopkeeper, and also shows how far you are to the next level of friendship (unlocking new abilities and items). The friendship you are currently at is shown in light blue, while the friendship needed to attain the next level is in a darker blue.

Although buying items that only need yen pins raise your FSG, quest items do not raise it.