Her C1 increases the efficacy of her Burst while her C2 slightly boosts all her Pyro damage.
These can be obtained by farming the two different kinds of Ley Line Outcrops around Teyvat, which only take 20 Resin each.
And as you look upon the same fireworks, many years later, that same memory and the feelings that came with it will surely rise again to the forefront of your heart.