Ultra Maniac OVA

Ayu Tateishi is a popular second-year student at her middle school admired for being calm, cool, and collected. But this carefully preserved image was all crafted to catch the eye of her crush Tetsushi Kaji, who once complimented her for those qualities. Studying, playing tennis, and finding chances to speak with Tetsushi are all that are on Ayu's mind—until the day she finds a mini-computer underneath a bench.

After returning the item to Nina Sakura, a girl who was searching for a lost item earlier, Ayu is chosen by Nina as a confidante for her secret. When the school's two tennis teams have a dispute regarding use of the courts, Ayu is forced to settle the matter by playing against Hiroki Tsujiai, the captain of the boys' team and Tetsushi's best friend. While dreading the prospect of losing and embarrassing herself, Ayu is approached by Nina, who is revealed to be a witch who came to Earth after failing to graduate from the Magic Kingdom's middle school. Wanting to help Ayu win the match, Nina imbues a piece of chocolate with a spell that just might come in handy...

(Source: MAL)