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.
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!
Currently there are no similar looking kanji which exist in the WaniKani learning system