Unused Effects
The unused effects may represent different interests/events/people in Rei's life, as they radically alter Rei's appearance to the point of him looking like a completely different person.
Bad Weather
There are hints that Rei is staying in his apartment due to bad weather. It's implied from his clothes and the space heater in his room that he's cold. Going to the balcony always shows cloudy and/or snowy weather. Rei could be snowed in his apartment and can't leave, or he simply doesn't want to leave his room due to the cold.