Wow many of you got the gadget correct! It is indeed a bamboo whisk, a chasen, for tea cermonies.
Icie’s was the most accurate description:
whisk is right, but it’s a bamboo whisk used for preparing maccha (thick japanese green tea) during tea ceremonies. green tea powder, hot water, whisk.
The Japanese tea ceremony is a formal celebration, with even the hand movements carefully dictated.
Other utensils used during the tea ceremony are the tea bowl and tea scoop.
Deeply rooted in Japan’s history and culture, the tea ceremony is an event one should try to partake in while visiting Japan.