Bakuon!! OVA

Synopsis

After Hijiri finally obtains her own motorcycle license, she has one final ride with Hayakawa, who experiences mysterious rejuvenating effects and reverts to a younger age, revealing his true identity as a female maid. Confused by the circumstances, Hijiri attempts to hide Hayakawa's identity when the others come over to visit to see her new bike. Jealous of Hayakawa getting everyone's attention, Hijiri rides off on her own, only to run into some trouble when her bike topples over. Remembering that which is most important, Hayakawa returns to her normal appearance as an elderly butler to help Hijiri.

(Source: Wikipedia)