The Book of Weeaboo Fightan Magic
Sometimes called Tome of Battle: Nine Euphemisms for My Dick, The Book of Weeaboo Fightan Magic is the nickname given to The Tome of Battle: The Book of Nine Swords, one of the more famous (or infamous) Dungeons & Dragons 3rd Edition (3.5) splatbooks. It introduced three new classes, Crusader (baby's first paladin, for the gamer who wanted to stab shit instead of playing support), Swordsage (which is probably the biggest source of the book's reputation), and Warblade, (which is, essentially, the fighter only comically better in every way) and a wide variety of abilities referred to as Stances and Maneuvers, which basically function as spell-substitutes for martial characters. Each of these abilities are all grouped into schools called Disciplines. This was supposed to lessen the power gap between martial and magical characters, which had the unfortunate side-effect of rendering all existing fighting classes kind of irrelevant (Not that they weren't already). Whether this is the fault of the authors or of the system they were working in is debatable. Either way, gee, thanks Monte Cook!
Opinion is divided on the quality of the content of the book itself. Some believe the Stances and Maneuvers systems are interesting and worthy additions to the game, whereas others consider them to be bizarre and illogical, comparing them to some of the ridiculous techniques seen in Japanese anime and manga. This comparison is what resulted in the book being assigned its nickname, which has indeed become so pervasive that even many who like the content call it Weeaboo Fightan Magic.
Of course, the people who complain about the book and the way it approaches swordfighting and martial arts as feeling too much like anime...need to actually read a historic swordfighting manual. Intricate and complicated techniques are very common in swordfighting regardless of the culture. In fact, German Longsword fighting was a very technical and at times esoteric discipline. This one style alone features complex training exercises, mental conditioning and yes, complicated techniques with very fancy names. These said techniques ranged from basic but tricky concepts (back or "false" edge cuts), to difficult but effective techniques with very "anime" purposes behind them (the master strikes where you are trained to "attack and defend yourself in a single motion") to the outright bizarre (unscrewing the sword's pommel and throwing it at the enemy). In other words; the concept isn't entirely "weeaboo", it's just a way of translating the complexities and intricacies of real life sword fighting. True, this book adds actual mystic elements to martial arts... but it's a Fantasy setting anyways. Regardless of what culture you're from if such a thing is accessible then you are going to take advantage of it.
None of the maneuvers are that game breaking. You gain only one save or die maneuver at level 17 (almost twice as long as it takes the spellcasting classes) which not all of the classes can use. Even that's peanuts compared to all the shenanigans a good Wizard or CoDzilla can do. As for the fact that it renders the Fighter and Monk obsolete, well... they were already very low tier to begin with, and it goes to show how shit the Monk was when they are made useless by the addition of ONE FEAT. If anything, this is actually one of the more balanced supplements, at least when compared to everything else in 3rd edition.
TLDR: It doesn't make the martial classes more powerful than the core rulebook's spellcasting trinity (Wizard, Druid, Cleric), it doesn't even really level the playing field. It just narrows the gap to something more reasonable.
If you're a Pathfinder player, then 3PP Publisher Dreamscarred Press has ported Tome of Battle to Pathfinder, under the name of Path of War. Included in the base book are three classes: Warlord (Better Cavalier with no mount), Warder (Better Paladin with no alignment restrictions), and Stalker (Ninja done right). There's also a supplement called Path of War: Expanded which brings in three more classes: Harbinger (An edgelord's wet dream), Mystic (Sort of a Sorcerer/Crusader hybrid) and the Zealot (TOUGH dudes who hook into the Psionics system that Dreamscarred Press also ported). There are further supplements that provide new classes like the Rajah (A heavily support-based combatant by using the Akashic system) and the Edgelord Archtype for Harbinger (they knew exactly what they were doing). Thankfully, these books also include Archetypes that allow some of the classes to also take a slice of that Weeaboo Fightan Magic pie, though none of them ever reach the sheer breadth of abilities that the full classes do.