User blog comment:St0mX/ Natsu & Dragon slayers aging theory discussion v2/@comment-25693405-20150817055000/@comment-26898341-20150817063423

Sting and Rogue are non-blood ( I think ) brothers so I'm pretty sure they've had about 99 billions opportunities to trade up each other's ability during say, intense training session but not once we see them use it. They are aware of its existence as they use it in Unison Raid but never individually. That goes to show that we have YET to see any Dragon Slayers use a technique that contain an element they don't come from just sucking in.