To give an example, a hot air balloon works by stuffing air in a huge bag and heating it up to reduce its density, allowing it to fly once its buoyancy exceeds its mass.

Rinnosuke-san, your drawings suck.

No, this is just how the world looks through my eyes.

Wind

Wind

You can also fly by using lift. It might be possible by using spiritual power to make some good wings and jumping forward fast enough.

Yes, and the formula to calculate lift is...

Speed squared ✕ coefficient of lift ✕ wing area ✕ air density ✕ 1/2. Which is to say...

Flight ability and air density are closely connected. The higher you go, the thinner the air gets, and your ability to fly suffers.

However, since this formula shows that speed is a larger factor than air density, that means you can fly higher by going faster.

Of course, that's only relevant if you've got wings of the appropriate shape, but... you're not a bird, so to be blunt, I suppose that's not realistic.

So what you're saying is that I need more speed.