This is a major Japanese holiday (Buddhist). Dates vary around the country, but center around the 13th to the 17th (although it is held in July in some areas). During the time of O-bon, a family's ancestors come back home for a visit. This means that all family members are generally obliged to make the trip back to their hometowns in order to participate in various family functions. Because so many people who live in Tsukuba actually come from other parts of Japan, O-bon can be fairly quiet around these parts. You will probably find that most of your Japanese friends have either left town or are extremely busy with family commitments. Many stores and services are unavailable during this time, especially smaller businesses.