This coming Friday, March 14, is Howaito Dei (White Day), when males follow the custom of reciprocating the Valentine's Day chocolates (or other gifts) they received a month earlier.
The nature of the o-kaeshi (reciprocal gift) depends largely on the category of relationship between giver and recipient. Chocolates, for example, would be classified as honmei-choko or giri-choko.
The former, honmei, derives from a horse-racing term that means the probable winner or an odds-on favorite, and is humorously used to describe a serious relationship.