They're the fruits of tilia miqueliana Maxim in Koishikawa Botanical Garden. Their green color and roundness is so beautiful and cute!
The problem is, however, that tilia miqueliana Maxim is called "Bodaiju" in Japanese, meaning "ficus religiosa" or "sacred fig," under which Buddha is believed to have attained enlightenment.
This confusion occurred due to the mistaking of a tilia miqueliana Maxim tree for a sacred fig tree by Myōan Eisai (1141 - 1215), a Japanese Buddhist priest, and as a result, many temples across Japan have planted tilia miqueliana Maxim trees, calling them "sacred fig trees." But Eisai is believed to have also brought the Rinzai school of Zen Buddhism and green tea from China to Japan. This offsets his misunderstanding!😊