
I am huge fan of Japanese pop music (Not anime music, those are two different things) because of this I tend to have two theme songs per character, one in Japanese and one in English so no one gets all mad at me 
Loki
Wake me up - Ayumi Hamasaki
I actually managed to find a video with English and Japanese lyrics, hurray.
There are a few lines in this song that really resonate:
And is had this kind of rocky vibe that works out too. I'm hella biased though, I think Ayumi Hamasaki is a genius.
As for English, it's this
BUT only the remix version I linked here. The original doesn't come across as angry and agitated as this remix does.
EDIT: I'll just put what I think I'm going with
Armi
Namie Amuro - Contrail
You can watch the video here: http://en.musicplayon.com/play?v=982991
The song is just amazingly uplifting and hopeful and has kind of a quirky style of lyrics that really work with Armi's somewhat strange behavior. Hell Namie is basically being Armi in the video, being some pied piper of hope and that is totally a skirt she would wear.
I'll put the English lyrics in spoilers here:

Loki
Wake me up - Ayumi Hamasaki
I actually managed to find a video with English and Japanese lyrics, hurray.
There are a few lines in this song that really resonate:
- There is everything, yet there is nothing, that is the law of this sandcastle
- The vacant memory remains like yesterday yet crumbles even more like my hair and makeup
- And within my calm, cold mind, I finish up the puzzle
- I can still be in time... while the wounds remain shallow
- Anyone can enter, yet no one can enter, that is the fate of this sandcastle
And is had this kind of rocky vibe that works out too. I'm hella biased though, I think Ayumi Hamasaki is a genius.
As for English, it's this
BUT only the remix version I linked here. The original doesn't come across as angry and agitated as this remix does.
EDIT: I'll just put what I think I'm going with
Armi
Namie Amuro - Contrail
You can watch the video here: http://en.musicplayon.com/play?v=982991
The song is just amazingly uplifting and hopeful and has kind of a quirky style of lyrics that really work with Armi's somewhat strange behavior. Hell Namie is basically being Armi in the video, being some pied piper of hope and that is totally a skirt she would wear.
I'll put the English lyrics in spoilers here: