I don't have much time to look into it right now, but the arguments presented - temperature data fudged, models too simple with tuned parameters - are not new, so you might be able to find rebuttals.
Interestingly it looks like climate deniers were citing this same fellow as predicting northern hemisphere temperatures would cool from 2015 (I suspect that to be a misinterpretation of Nakamura).
Time for warmist hari-kiri? Japanese researcher predicts cooler climate in Northern Hemisphere from 2015 – JunkScience.com