This event was distributed to commemorate the Japanese Cinematic release of Pokemon the Movie 20: I Choose You!
Serial codes for this event were being given away for pre-ordering the movie tickets, and another Pikachu can be redeemed if you have another code.
These serial codes are region locked to Japan 3DSes only.
This also marks the first time this variation of Pikachu is given away, as well as the first time that Pikashunium-Z can be obtained legitimately.
Distribution text describes the origin story of Ash and Pikachu leaving Pallet Town:
After the fateful encounter on his tenth birthday,
Satoshi (Ash) and Pikachu (Pikachu) depart from Masara Town (Pallet Town),
to set forth on their journey to become a Pokemon Master!
Format Ver.1.0.5-4, Post Updated Date:20171105_1703
Distributions of the same event: