Bleach: Ichigo's true Powers and why his zanapakto keeps changing its form?

While it was a subtle indicator, Zangetsu's ever-changing appearance represented Ichigo's understanding of his powers. No one's powers were cooler than the protagonist's, in this case, Ichigo Kurosaki's from Bleach, as is typical of most shonen anime. Ichigo was much more than he appeared to be at the start of the series, and it was later revealed that he was the son of a Soul Reaper captain and a full-blooded Quincy, both of whom possessed the Hollow known as White. As a result, Ichigo, their first child, is a human, a Soul Reaper, a Quincy, and even part Hollow hybrid, making him a truly unique being.

Ichigo's Zanpakuto, Zangetsu, represented his Soul Reaper powers as well as the foundation for all of his other powers. It also represented his ever-growing understanding of his powers and true nature. Zangestu's shape changed throughout the series. Ichigo underwent some kind of change or gained a better understanding of his potential every time this happened. The sword he used at the start of the series, for example, was never seen again after he unlocked his Shikai. This was due to the fact that the spiritual energy he was using was primarily Rukia's, with his own leaking out just enough to influence the sword's size.

The Soul Reaper abilities of Ichigo were unique from the beginning.

When Ichigo awoke his own Soul Reaper capabilities and was on the verge of becoming a Hollow, readers and viewers received their first real look of his genuine abilities. Even if the almost Hollowfication was now explained away, this was the first time the narrative even made a hint at Ichigo's true nature. His Soul Reaper skills began to emerge in a way that was unique from every other situation.

When they enlist in the group, all Soul Reapers from the Soul Society are granted Zanpakuto. These particular Zanpakuto are called Asauchi and were personally created by Oetsu Nimaiya. When these Zanpakuto are presented to their respective Soul Reapers, they don't really have any particular abilities because the Soul Reapers must imprint their own souls and power onto the blade. As each Zanpakuto has its own name, abilities, and spiritual energy, there are no identical Zanpakuto. But if he didn't have an Asauchi, how did Ichigo manage to do this?

Asauchi are created by fusing the souls of several Soul Reapers into the shape of a blade. This is also how Sosuke Aizen created the Hollow known as White, which infected Ichigo's mother and was eventually passed on to Ichigo himself. Instead of imprinting his power and soul onto an Asauchi, Ichigo imprinted them on the Hollow within him, transforming it into his Zanpakuto spirit. This explains why his inner Hollow resembled a completely white Ichigo.

source: animeworldnow