Swain Runes explained
There's one set of runes for Swain on patch 14.22 that is the clear favorite for LoL players and pros alike. The best Swain rune paths on the position 
Mid are 
Sorcery as the primary path and 
Resolve as the secondary path with a pick rate of 47%. Besides picking runes on Swain you should learn how to play Swain and if you are interested in pro matches take a look on how a pro builds Swain. If you want to discuss 
Swain then you should visit the champion subreddit.
Swain runes from primary path
Sorcery empoweres abilities of Swain and increases the available champion resources. Most of high elo players – and our LoL pros in the the major regions – have agreed that Summon Aery is the best keystone rune to run on Swain. This keystone rune adds more poke damage to your abilities. And additionally grants an extra shield, whenever Swain empowers or protects an ally with abilities. Other primary runes on Swain are Manaflow Band, Transcendence and Scorch.
This is usually followed up by taking Manaflow Band for additional mana and mana regenaration. Transcendence for some more Ability Haste. Scorch increases your control in the early game.
Swain runes from secondary path
When it comes to your secondary path, most Swain players prefer to go with Resolve. Resolve empowers the survivability of Swain and increases the tankiness. On the Resolve path, the best runes for Swain are 
Overgrowth and 
Bone Plating.
Overgrowth increases your maximum amount of health. Bone Plating make Swain overall tankier, by decreasing the amount of poke damage in the early game.
FAQ for Swain Runes
Which is the best keystone rune on Swain?
The best keystone rune on Swain is Summon Aery. This Swain runes setup is then referred as Swain Summon Aery.
What runes does Swain use?
Runes from the paths Sorcery and Resolve are the most used runes on Swain. For the exact pick rates of Swain runes used, you have to study the rune distribution presented.