よそよそしく describes behaving toward someone in a noticeably distant, reserved, or awkward way, as if you are not yet familiar with each other. In the song, GReeeeN recalls how the couple acted when they first met, contrasting their initial awkward distance with the deep understanding and shared life they later built together.
愛唄 (Ai Uta, "Love Song") is GReeeeN doing what they do best: a guy who knows he is being cheesy and says it anyway. He opens by admitting that saying 「愛してる」 ("I love you") is クサい (kusai). Literally that word means "smelly," but here it is slang for corny or cringey, the kind of line that makes your friends groan. Then he shrugs: there is no other way to say it. And she laughs at him, of course. 「ほらね! またバカにして笑ったよね」 ("See! You made fun of me and laughed again"). I love that the song lets her tease him.
The heart of it is simple. He is not sure she picked the right guy, but standing 隣 (tonari, "next to") her through days of crying and laughing has become his reason to live. He looks back at their first meeting, when they were awkward with each other (よそよそしく, yosoyososhiku, "distant, stiff, like strangers"), and the fights since. By the end he promises to hold her hand until his voice gives out with age, and to swear to God 「めちゃくちゃ好きだ!」 ("I love you like crazy!"). めちゃくちゃ is casual slang for "insanely" or "a ridiculous amount," which is exactly how a nervous boyfriend talks. He even calls his own song ヘタクソ (hetakuso, "terrible, clumsy"), which is a bit much, but it is also why the whole thing feels honest.
GReeeeN formed in 2002 in Koriyama, Fukushima, and its four members, HIDE, navi, 92 and SOH, have never shown their faces. All four studied dentistry at Ohu University and hold dental licenses, and staying anonymous lets them keep working as dentists at home.
Their 2008 single Kiseki became Japan's best-selling download single, with more than 2.3 million ringtone downloads. In March 2024 they left their management, went independent and changed their name to GRe4N BOYZ.