Because of Mary's death, Watson and Sherlock broke off their relationship, and Sherlock's life fell into a trough. At this time, the second ray of light in his life came into his life - Elia Spencer, a gentle and adventurous girl who likes excitement. She has the same reasoning level as Sherlock and extraordinary observation ability, which makes Sherlock's favorability towards her slowly increase... (Ahhh! I haven't figured out the plot yet, so let's talk about that for now)
Purpose: To make a major change in Sherlock's life