Anko is from the Japanese anko (餡子 — sweet bean paste) — modern formation. Anko Mitarashi is a character in Masashi Kishimoto's Naruto (1999-2014) and Naruto: Shippuden manga and anime franchise. The Naruto manga has sold over 250 million copies worldwide. Anko is a Konohagakure Special Jonin and former apprentice of Orochimaru — bearing his Cursed Seal of Heaven on her neck.
Anko does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
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In Pythagorean numerology the letters of Anko reduce to 5, The Seeker. This is a traditional interpretive system, not a factual claim about the name.