In Japan it used to be common practice to send gifts in summer (ochuugen) and/or in year-end (o-seibo) to the people who take/took care of you regardless of business or private. Nowadays this practice is being faded gradually,

You can buy the gift at department store

However, still many people are practicing. If you visit any department store during this season, you will find a special corner that has been set up for the gifts. The products are sold from food to goods for daily use. Most gifts are 2,000 yen ~ 10,000 yen.

If you wonder whether you should or not, ask your Japanese friend.