Star
The sun that gives life is our very own star (which we happen to call the sun). Of course, all the other stars are probably giving life to other planets as well.
Imagine all sorts of stars all around the universe giving life to planets as suns. These are all the stars you see in the sky and there are billions of them. I hope you don't feel overwhelmed by how minuscule we really are when you look up at all of them.
せい
ほし
None
This star (the sun) and all of the others are yours to protect with your trusty saber (せい). If you could protect your land from the West, then you can certainly defend the stars too!
Now you're soaring through between the stars, swinging your saber through the silence of space, and... wait. No that was a dream. You roll over and pat your saber. The two of you are ready just in case the stars need your help.