Japanese is a difficult language to many, so you have definitely come to the right place. There has been a lot of discussion online about what IMABI is and is not. Who else to find out what it is than the maker of the website!
Japanese has and will always be my passion. When I made the first page of this site in February of 2009, I didn't have a particular goal for the website. In fact, the first pages I made were oriented towards simple resource pages with Kanji-related pages being the initial focus. Grammar discussions, which is what comprises the majority of the site now, were still a ways off from being realized.
Late that summer in 2009, I began answering Japanese language questions that were left on music videos. Of course, that artists wouldn't have had the time nor the ability to answer their fans' grammar questions. What began as an innocent reply here and there resulted in receiving DMs asking me to go into further detail.
From those interactions via Youtube's messaging system at the time, a few of the friends I had made suggested I incorporate them into a website and see where it would go. Since I had already attempted making a small webpage, those messages became the first rough drafts of some of the first lessons recreated.
If you were to see a snapshot of IMABI at the end of 2009, it would've resembled a jumbled mess of approximately 20 pages, but ever since, the website has been under constant construction, becoming the massive collection of lessons it is today.
Since 2010, the website has undergone at least one major expansion project every 1-2 years. To accomplish this, 50 new lessons are typically created from content that has either already been slightly touched on or new topics suggested by users. Then, the curriculum is updated to reflect the latest content to further streamline the learning process.
Consequently, some lessons have received major work. Lesson 1 in 2010 was about loanwords from English as a basic introduction to the latent knowledge learners would already have, but as of 2021, Lesson 1 is solely about the vowels, but the words introduced are cherry picked to be both easy to say and those that someone might actually already know. Planning of this sort can span months and even years before they're orchestrated properly into the curriculum.
Starting in late 2018, I began working on the latest expansion project. The goal of this expansion is to completely repurpose Veteran 2 so that Advanced 1 through Veteran 2 focuses on content that can get a learner to easily pass the N1 of the JLPT while also understanding any advanced grammar topic they may come across in their studies.