>>725126978
The Kitasan + El Condor Pasa support card banner is what you're thinking of, and it will come near the end of December at this rate.
>>725127069
Not all gachas work like this, but in Uma, once the banner ends the character/support card is added to the pool for all future banners. It's just harder to pull them because they're not featured anymore and you can't roll 200 times to guarantee them because they're not featured. So while you can simply pull Fuji or whoever, you're far more likely to pull whoever is featured on the banner.