Kazuko is from the Japanese 和子 (Kazuko — kazu harmony/peace + ko child — harmony child, peaceful child). Kazuko is one of the Japanese feminine names — central to traditional Japanese heritage.
Kazuko 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.
In Pythagorean numerology the letters of Kazuko reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.