Hikari – Utada Hikaru (2002)
This is one of the more tenuous entries on this list. Since I can find nothing within the song’s lyrics referring to Kingdom Hearts nor any production history stating it was specifically written for it I would refute its status as a game-related chart hit.
Okay, so it was picked by KH director Tetsuya Nomura to be its main theme and was used to co-market the Square-Disney crossover game in Japan. But Blur’s ‘Song 2’ was used as the title theme for FIFA 98 but does that make it a best-selling video theme song?
Regardless, it’s still on this list as the majority of people you ask will argue that it’s an inexorable part of the game and the franchise. Japanese pop icon Utada Hikaru would later provide another song called ‘Passion’ (known as ‘Sanctuary’ in it’s English-language incarnation) for the theme tune of Kingdom Hearts II so you could argue that her and her work are a bit more invested in the series than a typical licensed song.
‘Hikari’ (renamed ‘Simple and Clean’ for the English localisation) was a huge hit in Japan spending three weeks at #1 in the Oricon charts, selling a total of 598,130 units. Guinness World Records lists it as the best-selling video game theme song in Japan, albeit it in one of their dubious ‘Gamer’s Editions’.
Utada would later maintain her connection with the video game industry in 2004 when she worked with Nintendo to promote the original DS with her song ‘Easy Breezy’.