Board Thread:Theories and Speculation/@comment-27295021-20180308000450/@comment-4974066-20180308005149

Merging 2 natures together is a Kekkei Genkai, yes. As stated, they cannot be learned except for in Rasa's case. It's also possible for 1 person to have multiple Kekkei Genkai. If a person with no Kekkei Genkai were to use 2 natures together, the result would just be some jutsu that has properties of both natures. An example would be Darui during the Kage Summit Meeting. When he attacked Sasuke, he used a jutsu called 'Lightning Release: Wave of Inspiration', which the 4th Databook describes as a fusion technique (融合術, Yūgōjutsu) that uses both Water and Lightning together without "merging" them. But Darui also has a Kekkei Genkai where he does in fact merge Water and Lightning, called Storm Release. Also merging 3 is a Kekkei Tōta, and theres only been one example so far of this ability called Dust Release which merges Fire, Earth and Wind.