Gift giving is a big deal in Japan.It is a tradition, and it is expected.Gifts are offered a sign of respect, appreciation and friendship. The gift that offered no need to be expensive, it can be the small yet meaningful ones where only the people that gives and receives will understand it's true meaning. Japanese are more emphasize on how a gift is wrapped and presented. Gifts are usually offered and presented with both hands and not opened when received. Japanese usually offer items in odd numbers but not in number of nine and number of four because they are unlucky numbers in Japan.
A good hostess gift is flowers, but don't present it in a large bouquet.
Do not give ilies, camellias, lotus blossoms, white flowers of any kind as they are associated with funerals. Do not give potted plants as they encourage sickness.