"Murder Your Darlings" by Chris Piascik; stuff available on society6.
on twitter as @umbrella_seller
Mycroft & Sherlock
Word Count: 4,033
Summary: Where Mycroft was smooth, Sherlock was sharp and keen as a knife-edge in body and in mind. Mycroft tried to be his whetstone whenever possible, because with nothing to sharpen himself against Sherlock tended to cut himself.