Toguro/Younger Toguro reveals his full power or 100 percent of his power in Episode 62/Season 2 Episode 37 of the Anime Yu Yu Hakusho with the title: “Toguro’s Full Power” or “Toguro’s 100 Percent Terror!” (According to Japanese translation)
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Toguro returns to the stadium after enduring a blast form Yusuke’s enhanced spirit gun. He expresses his disappointment as he was expecting Yusuke to be more powerful. Seeing his limited chances, Yusuke decides to remove the Spirit Cuffs given to him by Genkai.
The release of the cuffs removed the restraints it held on Yusuke’s power. He then surprises Toguro with a barrage of hits. Spooked by Younger Toguro’s eye expression he stops hitting him. After getting up he undergoes a transformation and reveals 100* percent of his total strength. The power increase was great enough that he could inflict damage to Yusuke with just the flick force of his thumb.
[*] It is noteworthy that although the title of the episode indicates Younger Toguro was at his full power he admits in Episode 64 that he was really at about 85% of his total strength at his first transformation. He also dies in episode 64.