Ichigo Kurosaki, the main protagonist of the anime and manga series "Bleach," has several forms and power-ups throughout the series. Among these forms, his strongest and most powerful form is commonly referred to as "Final Getsuga Tenshō."

Final Getsuga Tenshō is a transformation achieved by Ichigo during the final arc of the series. In this form, Ichigo gains an immense increase in power and abilities. His appearance changes, with his hair turning black and his eyes glowing red.

In this state, Ichigo's strength, speed, and spiritual power are greatly augmented. He gains access to an incredibly powerful attack called Mugetsu, which unleashes a devastating wave of energy capable of causing significant damage. However, using Mugetsu exhausts his powers, and he loses his Shinigami abilities temporarily.

It's worth noting that Ichigo has other forms and power-ups throughout the series, such as his various Bankai forms and the Hollowfication transformations. However, Final Getsuga Tenshō is generally regarded as his ultimate and strongest form, as it represents the culmination of his power and marks a significant turning point in the story.