Naruto merges his Rasengan with Minato's to create a Rasengan that drills through the opponent, causing massive damage. The Supreme Ultimate Rasengan, like the Tornado Rasengan, has several streams of chakra spiraling around the centre, but it has far more streams, completely covering the users' bodies. These streams are capable of deflecting attacks. The sphere itself appears unstable, with the shape fluctuating wildly unlike the solid sphere shape of other Rasengan techniques.
The Supreme Ultimate (太極, Taikyoku) is a Taoist concept which refers to the undifferentiated absolute and infinite potentiality, encompassing the entire universe.
Minato states that when two similar chakra are near each other, they resonate. And when they are combined, the strongest Rasengan can be formed.