You can learn to sing to it in Japanese, it’s easier than you can imagine actually. Oh, and that group is동방신기, a Korean pop group whose name is Tohoshinki in Japanese.
Doushite~ kimi wo suki ni natte shimattan darou
Donna ni toki ga nagarete mo kimi wa zutto
Koko ni iru to omotteta noni
Demo kimi ga eranda no wa chigau michi
Doushite~ kimi ni nani mo tsutaerarenakattan darou
Mainichi maiban tsunotteku omoi
Afuredasu kotoba wakatteta noni
Mou todokanai
Hajimete deatta sono hi kara
Kimi wo shitteita ki ga shittanda
Amari ni shizen ni tokekonde shimatta futari
Doko ni iki nori mo isshou de
Kimi ga iru koto ga touzen de
Bokura wa futari de otonaninatte kita
Demo kimi ga eranda no wa chigau michi
Doushite~ kimi wo suki ni natte shimattan darou
Donna ni toki ga nagarete mo kimi wa zutto
Koko ni iru to omotteta noni
Mou kaerenai
Tokubetsuna imi wo motsu kyou wo
Shiawase kao de tatsu kyou wo
Ki reina sugata de kami sama ni negatteru kimiwo
Boku janai hito no tonari shukufukusareteru sugata wo
Boku wa douyatte miokureba ii no darou
Doushite~ kimi wo suki ni natte shimattan darou
Ano no koro no bokura no koto
Mou modorenai (kangaeta~)
Doushite~ kimi note wo tsukami ubae nakattan darou
Donna ni toki ga nagare te mo kimi wa zutto
Boku no yoko ni iru hazu datta
Sono mama aii
Soredemo~ kimi ga boku no soba hanarereteite mo
Eien ni kimi ga shiawase de iru koto tada negatteru
Tatoe sore ga donna ni sabishikute mo