I watched the 1997 Berserk series in one sitting.

I fell in love instantly.

I watched all of naruto+shippuden over roughly 3 weeks.

Sort of thinking through my fingers here…

The first notable one I can think of is watching the entire run of Elfen Lied in a single sitting, so 12 episodes. I’ve done that a number of times since though, most recently with the first season of Zombieland Saga.

One curious one was Magic Knight Rayearth. I watched most of the first season - 20 episodes - in a single day, but not so much because I was so hooked on the story. What it was was that if I didn’t catch it in time at the end of one episode, the next episode would start, so the OP would start, and that was it. There was no way I could turn off what is, IMO, the best OP ever, so I’d end up just letting it go, which led into the episode, and so on. I’m not sure how many total episodes I watched that way though.

I can only think of one instance when I’m certain I watched more than a single season/cour in a single sitting, and that was The Apothecary Diaries. I watched the first half or so of the first cour of the first season one day, and it was certainly good, but it hadn’t yet fully hooked me. But then when everything started coming together in the second half of that cour, I couldn’t stop, and I watched the rest of it plus the entire 12 episode second cour in one long binge. I’m pretty sure that started from about the time that Maomao went home to visit her father, which was episode 7, so that’s 18 episodes or about 7 hours.

Not sure if it can be considered a binge since it took me multiple days (but still done in a werk or so) due to the sheer number of episodes, but it’s Pokemon Horizons for me. I believe it was at ~120 episodes when I caught up.

Second place would be Gundam SEED (inclusive of Destiny) which is ~100-episodes long.

What they have in common is that they are long enough to beat out other anime that are at most 24-episodes long. However, they are not so long as to be too daunting for me to even pick up (e.g. One Piece).

And to keep me watching episode-after-episode without feeling like stopping, they must have sufficiently strong hooks.

If it must be done in one sitting to be considered a binge, then plenty of one-cour (12-episodes long) anime tie for first place for me.

I think it was Season 3 of SNK. Watched the whole thing in a day lol

I can’t figure out how many episodes I watched in one session… but I finished Vinland saga in one weekend. Nothing TOO crazy but I feel like that’s all I did that weekend. It’s only 8 hours between two days I guess but it felt like much longer.

I watched the entire series of Case Closed over a single weekend.

Probably the time I watched all 26 episodes of Simoun in a day instead of studying for finals (it was a jam-packed semester and I needed a burn-out day. Plus Simoun is awesome)