Tamayo and Shinobu each play an important role in Demon Slayer's finale. What did they do to leave their mark?

Giyuu may not be very friendly or charming, but Demon Slayer fans love him for his cool kuudere ways and his amusing dynamic with Shinobu Kocho, who enjoys teasing him. Being the first Hashira ...

The Anti-Kibutsuji Drug ended up playing a huge role in the final battle against Muzan. How big of an impact did it make?