Yokai Watch is a very recent boom.
There was a comic and a 3DS game, which sold normally.(2012/2013)
The anime was the big influence.(2014) After the anime came out, sales of the game soared. The OP/ED songs from the anime became hugely popular, especially among elementary school kids. The kids loved the dances which went along with the songs. (I heard those songs everywhere in Japan when I was there last year. Small shops, big shops, shopping centers, theme parks, on tv...)
The collectible yokai medals were a hit too. People were scrambling to buy the DX Yokai Watch toy as well. The game sequels had great sales too.
It also hit a demographic similar to Pokemon.
This huge boom probably influenced Toei during planning/pre-production of both Ninninger and Ghost. though I'm sure they already had some similar ideas and themes floating around.
Ninninger's ending dance routine was in fact choreographed by the same person who choreographed Yokai Watch's 1st ending dance.
Last I heard, localized versions of the Yokai Watch games are being worked on and the first one is due to be released this year..and the anime is going to be localized too.