Just listen to current Japanese anthem...
https://www.youtube.com/watch?v=cMBbkjMM8p8

And compare it to this:
https://www.youtube.com/watch?v=o6wtDPVkKqI&has_verified=1

As you can see, current japanese anthem has only about 1 minute and it's slow and boring, meanwhile Cruel Angel's Thesis is modern song that can represent modern Japan. Also Japan is land and mother of anime and Neon Genesis Evenagelion is the classic one so its opening should be the best choice. In the end, all Japanese love this song so it is another reason why change current anthem to Cruel Angel's Thesis. 

Sign to this petition to make Naruhito (=Japanase caesar) notice that.