toguro (yu yu Hakusho)

The basis of their powers: demonic transformation and muscle manipulation.
After winning the Dark Tournament 50 years ago alongside Genkai and his older brother, Toguro requested to be transformed into a demon (upper-class B, but with potential that goes beyond what it appears). As a human, he was a martial arts master focused on technique and precision. After the transformation, he abandoned almost all of that in favor of pure strength.
His main power is Muscle Manipulation (筋肉操作 - Kinniku Sōsa, or "Muscle Manipulation"). He can channel his demonic energy directly into his muscles, controlling exactly what percentage of his maximum power he releases. This ranges from 0% (relaxed state, normal muscular human appearance) to 100%.
Visually, this works: With each percentage increase, it unleashes a burst of demonic energy (usually purple/bluish). Muscles swell dramatically, the body grows in size and mass, veins appear, and the skin becomes grayer/darker at high levels. The higher the percentage, the greater the strength, speed, durability, and stamina.
Advantages: He fights "controlled" most of the time, conserving energy and testing his opponent. He only releases more when necessary. This makes him unpredictable and intimidating — the opponent never knows if he's using 20% ​​or if he's going to jump straight to 80%.
Limitations: Even as a demon, the body has a physical limit. At 100%, it can still push itself beyond that (the famous "100% of 100%"), but this damages the body itself.
He doesn't need complex techniques. His philosophy is simple: "Strength that makes technique obsolete." He wanted such absolute power that technique, skill, or strategy would no longer matter. It's the opposite of what he was as a human being.
Power levels and examples in the Dark Tournament
Toguro displays the percentages progressively throughout the tournament:
20%: That's already absurd. A casual punch generates shockwaves that destroy the environment or send opponents flying for miles.

External appearance and first impression: the man of few emotions.
Younger Toguro presents himself as an extremely calm, relaxed, and composed man. He almost never shows emotion on his face. His default expression is neutral, firm, as if nothing in the world could shake him. He speaks directly, clearly, and without beating around the bush—never shouting, never making unnecessary drama. His only accentuated expressions appear in two specific moments: a slight smile or glint in his eyes when he is very happy (usually in exciting fights, against worthy opponents) or when he gets very angry (against "posers," dishonorable people, cowards, or those who break the rules).
This "ice man" facade makes him an intimidating antagonist from the very first encounter. He doesn't need to shout threats; his gigantic physical presence (muscles that grow with his power percentages) and low voice are enough. In the anime, he is even more stoic than in the manga (where he sometimes shows a more open, sadistic smile). This subtle difference reinforces that Toguro is a character who "contains" everything within himself.
Beneath this calm demeanor, however, lies a strong, self-imposed, and rigid moral code. He doesn't kill for pleasure. He prefers to avoid taking lives if the "job" doesn't require it. When he kills, he often apologizes afterward—an almost human trait that contrasts sharply with the demon he has become. He values ​​honor, courage, loyalty, and honesty. He hates those who cheat, those who are rude without reason, or those who pretend to be something they are not.
The original trauma: the seed of transformation.
To truly understand Toguro, we need to go back to the past. He was a great martial arts master, Genkai's partner and lover. Together, they ran a dojo and trained students. Toguro was already powerful, but still human—and already harbored a deep fear of aging, weakening, and losing control.
One day, the demon Kairen (or Kairin in some translations) invaded the dojo and massacred all of Toguro's students while inviting him to...