Released in April 2004 as Hirai's 20th single, looking at the translation of the lyrics, I realized that it was a bittersweet one about a man who no longer has the love of his life but still treasures the time that he had with her. And it was the theme song for the 2004 movie "Sekai no Chūshin de, Ai o Sakebu"（世界の中心で、愛をさけぶ...Crying Out Love in the Center of the World）whose plot was along those lines.
I never saw the movie but I remember that "Hitomi wo Tojite" got a lot of airplay on TV through the music shows along with shots of audience members tearing up. It absolutely hit the spot for everyone since it ended up becoming the No. 1 song of the year, sold over a million copies, went Double Platinum, won Song of the Year at the Japan Gold Disc Awards, was nominated for a Gold Prize at the Japan Record Awards and earned Hirai his 2nd appearance on NHK's Kohaku Utagassen (whew...that's the longest streak of Bold that I've used). I guess the only surprise I found out was that despite all of the accolades, it actually didn't hit No. 1 on the Oricon weeklies, peaking at "just" No. 2.
"Hitomi wo Tojite" was also a track on his 6th original album "SENTIMENTALovers" from November 2004. Unlike the single, it did hit No. 1 on the album weeklies and became the 3rd-ranked album of 2005.