This story is a sequel to The Chronicles of Summer Rain, Vol. 10 -- Ariel Dawn

Since becoming a Princess, Twilight's magical ability continues to grow by leaps and bounds. After cleaning in the restricted magical archives at Canterlot Library, Princess Celestia sends Twilight a box of magical fragments. When Princess Twilight stumbles across an ancient magical challenge, she jumps in with all four, and surprises even herself. But the spell she casts...