Why is NTR going so aggressive for Devara in Japan?
NTR has been promoting the film for the last couple of days in the Japanese market.;

Junior NTR followed up the success of RRR with his recent film Devara. Though the film was not a path, breaking sensation at the box office, it was a pretty decent face saving film for NTR after RRR. It could generate reasonably good revenues and turn out to be a hit at the box office.

In the meanwhile, it is now being reported that NTR is going all out for the promotional campaign of this Koratala Siva film, as he is actively promoting it in Japan.

NTR has been promoting the film for the last couple of days in the Japanese market, and he is even interacting with the local Japanese media as a part of the promotional campaign.

On the other hand, it can be noted that India was not as aggressive or abrasive with the promotional campaign in the Telugu states either. His promotions were rather very generic and confined to a small Telugu media circle rather than a wider press meet of a big proportion.
However, on the other hand, NTR is going absolutely bonkers for the promotional campaign in Japan as he is even dancing on stage and seen cheering for the local population. This could be a calculated attempt from NTR to generate international market for Devara so that he can happily proceeded with the second part.
This could be a calculated business decision to promote the film so aggressively in Japan in order to bring wider market to the film and make the sequel on a grand scale.
On the work front, NTR is currently occupied with War 2 and the film with Prashanth Neel, which is going to start the next schedule in the last week of March.