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White Day (ホワイトデー Howaito Dē ) is a day that is marked in Japan, South Korea, Taiwan, and China on March 14, one month after Valentine's Day.
In Japan 
In Japan, Valentine's Day is typically observed by girls and women presenting chocolate gifts (either store-bought or handmade), usually to boys or men, as an expression of love, courtesy, or social obligation. Handmade chocolate is usually preferred by the recipient because of the perception of sincerity, effort, and emotion put into a home-made confection. On White Day, the reverse happens: men who received a honmei-choco (本命チョコ?, "chocolate of love") or giri-choco (義理チョコ?, "courtesy chocolate") on Valentine's Day are expected to return the favor by giving gifts. Traditionally, popular White Day gifts are cookies, jewellery, white chocolate, white lingerie, and marshmallows. Sometimes the term sanbai gaeshi (三倍返し?, literally, "triple the return") is used to describe the generally recited rule that the return gift should be two to three times the cost of the Valentine's gift.
In other Asian countries 
There are slightly different White Day tradition in other Asian countries.
South Korea 
Boys or men give candies to girls or women; however, this is mostly between couples and lovers. It is a popular practice in Korean elementary schools for boys and girls to exchange lollipops and other candies with their friends of either gender on both Valentine's Day and White Day.
The tradition is opposite from that of Japan: on Valentine's Day, boys or men give chocolate to girls or women and the opposite on the White Day.
The White Day tradition is not as popular as in Japan.
White Day was first celebrated in 1978 in Japan. It was started by the National Confectionery Industry Association as an "answer day" to Valentine's Day on the grounds that men should pay back the women who gave them chocolate and other gifts on Valentine's Day. In 1977, a Fukuoka-based confectionery company, Ishimuramanseido, marketed marshmallows to men on March 14, calling it Marshmallow Day (マシュマロデー Mashumaro Dē ).
Soon thereafter, confectionery companies began marketing white chocolate. Now, men give both white and dark chocolate, as well as other edible and non-edible gifts, such as jewellery or objects of sentimental value, or white clothing like lingerie, to women from whom they received chocolate on Valentine's Day one month earlier. If the chocolate given to him was Giri choco, the man likewise may not be expressing actual romantic interest, but rather a social obligation.