You released the original version of Cave Story in December of 2004, just a few days before Christmas. Do you think there is a close connection between Cave Story and the Christmas holiday?
Pixel: I remember thinking, "Oh, well... it should be finished sometime, eventually," at least a year before that. But I just kept fixing bugs and making adjustments.
It's cold in December, and I was cooped up indoors, so I made a lot more progress. Maybe it was just a coincidence that it was ready for Christmas. 
Do you think your life would have been different if you hadn't decided to team up with Nicalis and bring Cave Story to a global audience on new platforms?
Pixel: Of course! I made the free version by myself, but so many new things have happened with Cave Story because of other people besides me. 
When the free version came out, I saw the reactions from many different players. I watched as the game brought them happiness, and I noticed when they started to lose interest. I expected that Cave Story would eventually be forgotten. But thanks to Nicalis, the game continued to earn more recognition. Cave Story's lifespan grew even longer, because it became available to players who don't own computers. And that success made it possible for me to continue making games as a full-time developer.
The Mimiga named Santa is the star of the new spinoff game Cave Story's Secret Santa. What do you recall about the origin of the Santa character?
Pixel: I think I named him Santa because he was the third Mimiga that I made. [Note: "San" means three in Japanese.] But in the Bushlands, where Santa makes his appearance, there's a mission where the player has to go through a fireplace. I didn't realize it at the time, but maybe I was subconsciously thinking about Santa Claus.
Hypergun: Are you surprised that the Cave Story characters you created are still popular, appearing in new games and fan art even 17 years later?
Pixel: [Searches for "Cave Story" on Twitter] Oh, my... I guess they are! Thank you! 
Cave Story Trivia

Pixel wrote the main Cave Story theme music (a.k.a. the Plantation theme) before he started designing and programming the game itself. 

The "Misery possession" music from Cave Story was remade as the "secret boss" theme from Studio Pixel's vertical shooter Guxt.

That same tune was also remade as the "Possessed Nanao" boss theme in Studio Pixel's platform/shooter Kero Blaster!

Santa appears in a Santa Claus suit if you play Cave Story+ between December 24 and January 6. And that's not the only change you'll see during the holidays....