Board Thread:Wiki Operations Questions/@comment-136370-20150102091313

I don't read enough Japanese to have a personal stake in the matter, but here's Over-Time's rationale on the matter:

“Why’s there that dumb J in Ninninjer?” – The katakana for -nger series has always been -njyaa. Toei decided to lay down wordplay as the Japanese are wont to do with a name that can be read as a portmanteau of ninja and ranger. So there’s our own.  