40 seconds after writing a name in the Note, the person dies. Because Four Is Death, Death Note has 4×10 n.In Darker than Black the number 201 (Hei's Contractor Messier Code) tends to find its way into everything.It's associated both with the protagonist, Kudou Shinichi (fittingly a modern adaptation of the Sherlock Holmes archetype), and with the main antagonists, the Karasuma Group, who developed a drug with those serial numbers that they used as a poison and subsequently dubbed it 'the Experimental Detective.' In a twist of irony, their first human test subject for the 4869 batch was, by complete coincidence, Kudou Shinichi. Case Closed has '4869,' the Goroawase Number for 'Sherlock.' It's been used frequently as a password for various devices and as code numbers and even, in the anime, as a license plate (before that was retconned).And apparently after 9 days, he'll regain the world. After 90 years, he regained his ability to reason. After 900 years, he regained a heartbeat. Yhwach seems to function in relation to the number nine: he was sealed for 999 years. The number 9 also keeps cropping up, especially in the Thousand Year Blood War arc.

Tite Kubo also admitted the Quincy name partially derives from the Latin word for 'five'.

Later on, they reveal they've designated five Special War Potentials that they take very great interest in (Ichigo, Kenpachi and Aizen are quickly confirmed, Yamamoto is quickly excluded, the identities of the remaining two are not revealed for a long time). There are also special attacks that utilise five Seele Schneiders to pull off. Their cross motif is a five-pointed cross that can appear in both pentacle and pentagram formation. The Quincies are dominated by the number 5.In the Thousand Year Blood War Arc, the Royal Guard is sent to pick up the pieces of a demolished Gotei 13, and sure enough, there are five members in total (Ichibei, Senjumaru, Ouetsu, Kirio and Tenjirou). In response to an effort by Urahara, Isshin and Rukia during the Lost Agent arc, the Shinigami sent five representatives to rescue Ichigo (Byakuya, Renji, Kenpachi, Ikkaku and Hitsugaya). The Arrancar arc had five invaders (Ichigo, Uryuu, Sado, Renji and Rukia).

The Soul Society arc had five Ryouka (Ichigo, Orihime, Sado, Uryuu and Yoruichi).

Every time the protagonists need to engage in a rescue there are always five members.

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