チリヌルヲワカ / Chirinuruwowaka: 陰日向 / Double-Faced

Check out KOH3956's awesome cover of this song! 

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Title: 陰日向 / Kagehinata / Double-Faced
Band: チリヌルヲワカ / Chirinuruwowaka
Album: アヲアヲ / Awoawo
Lyrics: ユウ / yuu
Composition: ユウ / yuu
Japanese lyrics: http://petitlyrics.com/lyrics/2409582
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This song has some really interesting writing. There's a clever use of synonyms that sound similar, but have slightly different meanings all over this song. (隙間/狭間, 衝動/行動/鼓動)
The song also uses the expressions 雲行き (Movement of the clouds) and 風向き (Direction of the wind) at different points in the song. Again, these are similar and theme, and are actually both metaphors for "the situation" or "the outlook of things".
Finally, there's the part about becoming a shellfish. I couldn't find this as a common expression, but I did find one interpretation of the expression in an unrelated context. It can mean to not talk to anyone, not be affected by anyone, and simply live in your own shell. So the singer says: "When you feel like pulling away, come see me and I'll make you feel better".
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漢字	ローマ字	英語
影と日向の隙間を旅して	Kage to hinata no sukima o tabi shite	Travel in the chasm between shadow and sunlight
雨に怯えているの？	Ame ni obieteiru no?	Are you frightened of the rain?
雲行きなんて一夜で変わる	Kumoyuki nante ichiya de kawaru	The movement of the skies change overnight
空になったらすぐ会いに来てよ	Kara ni nattara sugu ai ni kite yo	Whenever you become empty, come see me right away
たちまち溢れる衝動	Tachimachi afureru shoudou	I'll give you an overflowing impulse right away
完璧じゃないからお互いに	Kanpeki ja nai kara otagai ni	We're able to communicate
通じ合えるのさ	Tsuuji aeru no sa	Because both of us aren't perfect
西と東の狭間に立たされ	Nishi to higashi no hazama ni tatasare	Being made to stand on the gap between east and west
明日を恐れているの？	Asu o osoreteiru no?	Are you afraid of tomorrow?
風向きなんて一夜で変わる	Kazamuki nante ichiya de kawaru	The direction of the wind changes overnight
貝になったらすぐ会いに来てよ	Kai ni nattara sugu ai ni kite yo	When you become a shellfish, come see me right away
気持ちを高める行動	Kimochi o takameru koudou	I'll make you feel better
薄紅色に染まる頃には	Usubeniiro ni somaru koro ni wa	When dyed pink
開き直っている	Hirakinaotteiru	You become defiant
切り札なんてきみの存在そのもの	Kirifuda nante kimi no sonzai sono mono	Your very existance is a secret weapon
人生なんて一夜で変わる	Jinsei nante ichiya de kawaru	Your life changes overnight
錆になったらすぐ酸化してよ	Sabi ni nattara sugu sanka shite yo	When you become rust, oxidize right away
次第に溶け合う鼓動	Shidai ni tokeau kodou	Movement graudally melts together
星になってもまた会いに来てよ	Hoshi ni nattemo mata ai ni kite yo	Even if you become a star, come meet me again
ありがとう、と伝えたい	Arigatou to tsutaetai	I want to say "thank you"
神は何度も微笑まないから	Kami wa nandomo hohoemanai kara	Since God never smiles at me
信じられるのは	Shinjirareru no wa	The only one I believe in
きみしかいないよ	Kimi shika inai yo	Is you

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Image is from Chirinuruwowaka's website