Letters From Across the Universe (слэш)

Unable to make friends on Vulcan, Spock signs up for Starfleet’s Intergalactic Pen Pal System, where one can seek new friends and experiences on other planets.
Choosing Earth, Spock gets matched to one Jim Kirk.
For years, they trade letters back and forth until one day Jim suddenly stops responding.
Spock then turns down a spot at the Vulcan Science Academy and heads to Earth to join Starfleet in hope of finding out what happened to Jim.