What is White Day?
One thing I have learned from manga is the existence of something called "White Day", which seems to only exist in Japan (and Korea, according to lemontart). I find it an interesting custom but can't help but feel that this is capitalist marketing at its finest:

It is widely believed that White Day was invented in the late 1970s by a candy-maker in Nagoya as an occasion for men to repay their lady-loves for Valentine gifts the previous month. Japan has developed its own, distinctive tradition for Valentine's Day, when women alone lavish chocolates and other presents on their sweethearts, or even on men they work with. The confectionery industry saw a lost opportunity here and firms such as chocolate maker Morozoff began promoting White Day in 1978. Handkerchiefs became an alternative gift idea. By 1991, the phenomenon had grown to the point where, according to a survey by the Osaka Marketing Information Research Office, Japanese men spent $330 million on White Day gifts. The average unmarried office employee shelled out $105 on women friends and colleagues, the survey showed. Yumi, who has worked in an office for 14 years, estimates her White Day handkerchief collection now exceeds 80.

Basically, the women give out chocolates (often handmade, as I have been led to believe, though who knows if that's true or not) on Valentines Day, and one month later, on White Day, the men who received chocolates give presents back to those women. Theoretically. What do you think?

Lingerie makers jumped on the bandwagon in 1985 and they too now furiously promote the festival. For 1993, one manufacturer, Wacoal, offers hot pink T-back knickers with the slogan "Intellectual Sexy Elegance." Another pair of panties, in red high-cut lace, is emblazoned "I Want to Express my Sober Feelings for You." A third depicts seeds for "planting together," while perhaps the smartest gift box proclaims "Your Inner Charms are Best Brought Out with Silk." (Reuters)

HAHAHAHA. Who wouldn't want a pair of red lace panties that express a man's sober feelings for you? I won't even touch "Planting Together" (mmhmm, you'll be planting something, alright) - yeah, I'm going to stop here before this turns NC-17 and I get flagged.

ETA: Black Day, for singles.