Answer: Boktai

In the fall of 2003, Konami released a rather innovative title for the Game Boy Advance and Nintendo DS centered on the adventures of a young man who, through a twist of fate and the actions of his father, has become a vampire hunter. Called Bokura no Taiyo (or Our Sun) in Japan, the title was condensed and anglicized to Boktai: The Sun is in Your Hand for Western audiences.

What set this game apart from any other at the time was that it incorporated elements of the physical world into the game play, including using the local time to adjust game difficulty (easier to slay vampires during the day, for example) and, most notably, a tiny solar panel that detected the presence of sunlight. Only by playing the game in direct sunlight could you gather solar energy to charge your weapons and help the protagonist in his battle against the vampires.

The solar-panel mechanic was used in subsequent games Boktai 2: Solar Boy Django and Shin Bokura no Taiyō: Gyakushū no Sabata(Japan only release).