Kayn Runes explained
There's one set of runes for Kayn on patch 14.21 that is the clear favorite for LoL players and pros alike. The best Kayn rune paths on the position 
Jungle are 
Domination as the primary path and 
Inspiration as the secondary path with a pick rate of 75%. Besides picking runes on Kayn you should learn how to play Kayn and if you are interested in pro matches take a look on how a pro builds Kayn. If you want to discuss 
Kayn then you should visit the champion subreddit.
Kayn runes from primary path
Domination improves burst damage and assassination tools on Kayn. Most of high elo players – and our LoL pros in the the major regions – have agreed that 
Dark Harvest is the best keystone rune to run on Kayn. This keystone rune gives you additional damage throughout the match. Other primary runes on Kayn are 
Sudden Impact, 
Eyeball Collection and 
Ultimate Hunter.
Sudden Impact increases your damage after dashing or being invisible. This is due to how easy it is to activate on Kayn with the amount of ways he has to dash, jump or going invisible. The additional lethality helps to take down the priority targets that much easier. Eyeball Collection is next up. This grants the user additional damage with every killing they score. Ultimate Hunter scales up Kayn ultimate haste on every unique champion takedown.
Kayn runes from secondary path
When it comes to your secondary path, most Kayn players prefer to go with Inspiration. Inspiration opens creative opportunities on Kayn troughout the match. On the Inspiration path, the best runes for Kayn are 
Cosmic Insight and 
Magical Footwear.
Cosmic Insight grants summoner spell and item haste. Magical Footwear allows Kayn to focus on those essential core items without the need to spend the additional 300 gold on boots.
FAQ for Kayn Runes
Which is the best keystone rune on Kayn?
The best keystone rune on Kayn is Dark Harvest. This Kayn runes setup is then referred as Kayn Dark Harvest.
What runes does Kayn use?
Runes from the paths Domination and Inspiration are the most used runes on Kayn. For the exact pick rates of Kayn runes used, you have to study the rune distribution presented.