I have an N2 & N1 grammar book that I'm working through and very near the end of.
I like the book because there is no English in it, and it is very simple - Grammar structure + 3-5 example sentences, about 10 structures per chapter, followed by 30-odd multiple choice, fill-the-gap sentence questions to test comprehension. My ex had scored herself on these questions, so I need to keep a sheet over the options so as not to know the answer, which makes it a bit harder because I can't see the options and have to try to guess which of the 10 structures goes in the gap and how it is conjugated etc.
Despite having the book for over 10 years, I only really starting going through it about 1 year ago. I decided it was time to finally at least "see" all the grammar structures in Japanese up to N1 level. I felt that if I could at least say to myself that I had seen them all, then it might give me more confidence.
I'm almost at the end - 2 N1 chapters left to go - and I feel like that need has been met. Basically, when I am listening to native level Japanese now, I don't have a nagging fear in the back of my mind that if only I had studied all the grammar, I would be able to understand.
Does this mean I understand the native-level Japanese fully? - Absolutely not!! But I feel like I can just focus on new vocabulary and phrases that I don't understand now - of which there are still many.
The more I study, the more I realise that I need to study more. Haha. Is this a virtuous circle?!