Shin Kanzen Master Grammar for the Japanese Language Proficiency Test (JLPT) N1

Shin Kanzen Master Grammar N1 covers 157 grammar forms for the JLPT N1. The book is divided into three parts: an introduction to the question formats and how to approach them, a skills development section that covers all three grammar question types on the JLPT, and a mock test. Grammar forms are organised by meaning and function, so patterns that are easily confused are studied together. Explanations are in Japanese only. Answers are in a separate 7-page booklet.

This is the strongest book in the N1 set and the one most consistently recommended for N1 preparation. The grouping approach is what earns it that reputation: at N1, many grammar forms are close enough in meaning that you need to study them against each other to tell them apart, and this book is built around that. The answer key doesn't always explain why a wrong answer is wrong, but that's a common frustration at this level regardless of which book you use. For N1 grammar, this is one of the best options available.