Yuhara could say something like that without batting an eye, because to him, this was not a matter of shame. This explanation concerned his survival and his plans for the rest of his life, so of course he had to claim that Rasenshuriken was his original creation.
To put it in a lofty yet down-to-earth way, what was the most likely stepping stone for someone from the lower classes to rise throughout history? Nothing more than "talent."
In Yuhara's case, talent "borrowed" from others was still talent.
"I was inspired by celestial bodies and astronomy. In the universe, massive celestial bodies capture smaller ones, turning them into planets or satellites. So long as you place high-mass Chakra at the center, scatter low-mass Chakra around it, and then apply a rotational force to the latter... the technique takes shape.
"The key is that part of the Chakra must have a sufficiently high density."
As Yuhara spoke, he spread his palm. A Rasengan appeared in the center of it... What he held did not seem to be a Rasengan, but rather a miniature model of a galaxy.
And truth be told, although the technique looked the same, its release principle and method of formation were completely different.
At first glance, Yuhara's absurd theory actually sounded quite convincing. In reality, however, the reason he could use this technique lay in his special ability to control Chakra, which had little to do with astronomy.
Because he used a special method, learning Rasenshuriken was at most as difficult for Yuhara as a B-rank Ninjutsu. Its main difficulty lay in increasing the Chakra's density and preventing self-inflicted damage. As for Rasenshuriken's form and nature transformation, those were actually secondary to him.
The Fourth Hokage pondered for a moment, then suddenly understood. "The sun and the planets?"