Neku wakes up in the Station Underpass on day 2 of week 1. In this location Neku learns about various pins and encounters yellow noise and support reapers for the first time. Neku later returns to this location on his way to defeat the first gamemaster.
Neku learns of the location of the Shibuya river here in week 2 day 5. This is also where Kariya guesses that Joshua is a living player.