Number One comes from the Bleach anime soundtrack and is closely tied to Ichigo Kurosaki, playing when the stakes rise and a battle turns in his favour. Fans first shared it through anime music videos and episode clips, then creators reused the short, punchy section for edits, memes and hype videos across social platforms. Its instantly recognisable brass riff makes it useful even for viewers who have never watched Bleach, much like Giorno's Theme from JoJo's Bizarre Adventure. That mix of nostalgia for long-time fans and immediate energy for new listeners keeps it in regular use.