やるせない describes a deep, frustrating sadness or emotional helplessness that you cannot easily express or resolve. In the song, the singer says he is still fighting this やるせない何か, capturing an unnamed inner pain that he continues to face while believing life has meaning.
Mrs. GREEN APPLE open this one with a little rule for life: "孤独を知って 愛を知る" (Knowing loneliness, I come to know love). You only understand love once you have been lonely. Then the logic gets sweet. "五感 働いて 君を救う" (With all five senses at work, I save you), and "それはつまり 僕も救う" (Which means I save myself too). Helping you and helping me turn out to be the same thing, because "結局僕らは人と人" (In the end, we're all just people).
The chorus is the part that sticks. "I love you の先へ" (Beyond I love you) is a lovely bit of mixed English and Japanese: の先へ means "to what comes after", so the singer wants to go further than the words "I love you". Then comes the relief of "僕はもう独りじゃないね" (I'm not alone anymore, am I). That ね at the end is a soft "right?", like he is checking with you and smiling. And "Upbeat で闇を晴らして" (Clearing away the darkness with an upbeat) is basically the song describing itself.
It is not all sunshine, though. The verse admits that "生きることのひどい痛みには意味があると信じてる" (I believe there's meaning in the awful pain of living), and the word やるせない in the next line is a great one to learn: it is that heavy, helpless, nothing-I-can-do feeling. The answer the song gives is cheerful stubbornness. "僕は僕をただ更新して" (I just keep updating myself) sounds like a phone software update, and I love that. "雨に唄ってスイングをして" (Singing in the rain and swinging along) nods to the old film Singin' in the Rain, and "希望とシェイクハンドして" (Shaking hands with hope) borrows the English "shake hand" straight into Japanese.
By the end the title makes sense: after "繭に包まれた人の夢" (A person's dream wrapped in a cocoon) and "鏡を見つめ直して" (Looking into the mirror once again), he arrives at "真新しい自分" (A brand new me). Out of the cocoon, brand new.
Mrs. GREEN APPLE is a Japanese pop-rock band from Tokyo, formed in 2013 by vocalist and songwriter Motoki Ohmori. They made their major-label debut in 2015 with the mini-album Variety on EMI Records.
Since the start of 2022 the band has been a trio: Ohmori, guitarist Hiroto Wakai and keyboardist Ryoka Fujisawa.