Even if you see responses from 987,983 people that say, "ZOMFG Nippon pistons are the bestest" or "OMGlolWTRFBBQ Nippon pistons will explode and kill your whole family", your BEST and MOST WISE course of action is to use whatever pistons your builder recommends based on his experience. Reasons for this:
Honda Motorcycles and Scooters India Limited (HMSI) for now is the other manufacturer who is setting up their plant in this location. Apart from this most motorcycle component manufacturers are setting up shop at Narasapura as well. Nippon Piston Rings the famous Japanese piston ring maker, has also shown their interest of setting up shop at Narasapura.
I've heard almost nothing about these Nippon pistons, but my guess is they aren't coated for FRM compatibility, which means you'd need to have the block sleeved to run them properly.
Now, having said the above....take a deep breath. Have some refreshing Earl Gray Tea and hear what I'm saying. We can answer MANY questions here, but some we refuse to answer as there is no answer (What color car should I get being an example) and some are best left to professional such as piston selection. Also, I actually wrote a post called . I know WAY more than the average bear about Subaru pistons and have NEVER heard of Nippon Racing Pistons and using google, you get like 4 results for them. Now type in CP Pistons or JE Pistons and you'll get 987,843 results. NEVER choose a no-name unknown brand for pistons.