shelgon:

A new event has begun. This event gives various hat Pikachu and can be obtained on American, European and Japanese 3DS games including Ultra Sun & Ultra Moon. This runs from today until December 1st. The codes are as follows:

• Hoenn Cap – LETSGOPIKACHU06
• Sinnoh Cap – LETSGOPIKACHU09
• Unova Cap – 13LETSGOPIKACHU
• Kalos Cap – LETS17GOPIKACHU
• Alola Cap – LETSGO19PIKACHU

Source: Serebii