The Umbrella Academy Season 3 introduced the Sparrows, the seven Hargreeves siblings of a different timeline, that our main characters encountered when they thought they'd returned to their own time. Christopher might be Number 7 in the new hierarchy, but his powers aren't to be underestimated. Why is Christopher a cube, though?
Christopher might have been deemed as Number 7 is terms of his usefulness to Reginald Hargreeves. Still, Christopher's powers can be quite terrifying.
In Netflix Geeked 2021, Christopher was described as "a telekinetic cube that can turn the room freezing cold and induce paralyzing fear without so much of a warning. The trustworthy, loyal oracle of the Sparrows is treated as just another sibling."
Indeed, the Sparrows don't seem to treat Christopher any differently because of his cube status, with Ben going for drinks with him early on.
While he doesn't speak in any way that the audience or even outsiders can understand, Christopher's siblings seem capable of understanding him, and his sentience can't be denied.
For a little while, we almost thought that Christopher would be able to contain the Kugelblitz within himself and save the world from the apocalypse.
Even the fact that he held it as long as he did makes him a particularly strong character but, ultimately, he succumbed to it and got consumed.
Why Is Christopher a Cube in The Umbrella Academy?
Christopher's nature as a cube is not explained in season 3 of The Umbrella Academy. It is unknown whether he always had this form, or if he acquired it later on for any reason.
It's a bit difficult to imagine that a human woman would give to a cube but, then again, it's also very odd that so many women who weren't pregnant before gave birth to overpowered children at the same time.
If Christopher has always been a cube, this might be a particularity associated with his powers. His shape might have even made him an attractive option for Reginald Hargreeves, as, by that point, he had proven that he isn't any good at bringing up human children.
Of course, several backstory elements in The Umbrella Academy remain a mystery, including why Ben Hargreeves died in the original timeline.
Other Sparrows and Umbrella Academy members bear different forms of physical deformities; Luther has an ape-like body, and Alphonso has extensive injuries that apparently got worse over time if the flashbacks are any indication. We don't know if Fei had eyes at any point, but her scarred face suggests that she might have been injured at some point.
Besides, in Season 1, Reginald has proven that he is not beyond causing his adoptive children physical pain if that would help his plans or harden them.
All the above make it possible that Christopher wasn't always a cube but became one at a later point due to some form of experimentation. While Christopher died in Season 3, he might still appear in a future season as the timeline was reset once again.