To Love ru ova 3 is filler:

In a sense all the to love ru ova's are filler, in that they add in random things and get various details wrong.  Because there's a subtle gap between a good and a bad scene, every minor detail counts.  When you get so many details wrong so often it ruins the overall experience.  But at least ova's 1-2 and 4-6 have some basis in the manga.  (ova 5 is really stretching it. . .as far as I can tell only the first couple minutes are canon)  Ova 3 is a plain abomination.  It's pure fanservice and makes no sense.  It would probably be best to steer clear of all the to love ru ova's and simply read the manga from start to finish, but at least skip ova 3.

Even Motto To Love ru gets some details wrong in its adaption, so there's really no solution except to read every single chapter of the manga.  And of course, most of the chapters of To Love ru were never adapted.  I think the Darkness anime adaption was much closer to the source and more thorough, but I recall it missing many chapters and details too.  I don't think you can safely skip reading any chapters of To Love ru, even Darkness should be imbibed in manga form.

My re-read of the entire To Love ru manga is now finished, but that still leaves Darkness to read.  While the manga is fresh in my mind I also want to watch the Motto To Love ru anime and make sure it's all canon.

Most of the chapters of To Love ru are kinda aimless and fruitless, 'ecchi of the week' type adventures.  But sometimes they spur important character development and plot development, which always leaves a nice fluttery feeling in your heart.  I love it when people get closer or understand each other better.

Mangaka have a tough job, every week they're required to come up with a new idea and get it down on paper to appease the ravenous audience.  Plus so long as the story is popular the editors encourage the authors not to finish the story but somehow drag it on through various contrivances.  So you end up with a lot of pointless chapters, you could call them 'manga filler.'  They're canon, but they may as well not be, since nothing worth reading about actually happened in them anyway.  I sympathize with the author, but I really think this culture of 'whatever sells' should go by the wayside.  Demon Slayer made use of every single chapter to advance the plot.  There's no wasted motion.  And it's the highest selling anime movie of all time.  People notice.  We can tell when you're trying to tell us a story, and when you're trying to waste our time.

I feel like the memorable, heartwarming moments in To Love ru could have been covered in half as many chapters, or even fewer.  Maybe then the story would have received a faithful adaption as the animators put more faith in it selling to the audience 'as is.'  Well, too late now.  The odds of a To Love ru remake are right down there with a Ranma 1/2 remake. . .