Koyuki is a friend of Haruhi and Anri who is one year above them and is also in the magic section. Her magic wand is named sphere Tom (スフィアタム, Sufia Tamu?) though it is also known to be nicknamed "Tama-chan" (タマちゃん?). It takes the form of a staff with a small green sphere on the end that floats on the staff. Unlike the other magic wands featured that can speak spiritually, sphere Tom has a face from which to voice its opinions.
Koyuki inherited the craft of making "Tama-chan"s and puts a lot of effort not only into their creation but going as far as to remember the order in which she made each one despite them appearing all to be relatively similar in appearance. As this dedication to magic has shown, she seems to be very skilled in her use of magic, especially divination magic or fortune telling.