Here's why "One Day, We'll Meet Again" is so popular:
* Nostalgia: It's the theme that most fans associate with the core of the Inuyasha anime.
* Catchy tune: The song's melody and lyrics are easily memorable and evoke strong emotions.
* Emotional resonance: It perfectly captures the bittersweet nature of Inuyasha's journey and the longing for reunion between the characters.
* BoA's popularity: BoA was a very popular singer in Japan at the time, and her voice lent a unique and memorable quality to the song.
While "My Will" is also a great theme, it's associated with the later, more action-packed arcs of the anime, and doesn't have the same nostalgic appeal as "One Day, We'll Meet Again."