There are many places in Tokyo where to spend a great Valentine’s day, but for a romantic evening stroll, I think I would choose Shinjuku Southern Terrace.
Since November, and lasting exactly until the Valentine’s day, on February 14th, between 5PM and midnight, thousands of white and blue lights are creating one of the most beautiful winter illuminations from Tokyo:

Shinjuku Southern Terrace Winter Illumination, Tokyo

EXIF Info:

Yesterday’s Japan Photo: Astro Boy from Takadanobaba