Fairy Tail (OVA)

Lucy investigates a suspiciously rewardless job posting that requests a female recipient to come to Fairy Hills, Fairy Tail's all-female dormitory. The client, dorm matron Hilda, asks Lucy to find a missing box on the property; to Lucy's indignation, Hilda forces her to wear a skimpy cat costume while doing so. [Source: Wikipedia]

In an alternate setting, Lucy is a transfer student at Fairy Academy, where Fairy Tail's members are depicted as high school students, and Happy and the celestial spirits serve as teachers and staff. Erza, the student council president, asks Lucy and fellow transfer student Wendy to help her prepare for a date with Siegrain. En route to her date, the three are harassed by Gajeel and the Element 4 from the rival Phantom Academy. [Source: Wikipedia]

While cleaning the guild's storage, Natsu has a traumatic memory of an event in which he received the scar on his neck. This activates a magical book called Memory Days, which transports Natsu and his friends back six years in time to the day from Natsu's memory. [Source: Wikipedia]

Mavis' spirit leaves Sirius Island to visit Fairy Tail, watching as Natsu and his friends train for the Grand Magic Games. That evening, the girls drink all of the alcohol at their lodging and tease the mortified boys in a drunken state. Later, at the hot spring, Lucy tells the girls about how she first discovered Natsu and Happy's house. In a flashback, Lucy plans to play a prank on Natsu and Happy by waiting in their room as revenge for the many times they have appeared uninvited in her own home. She is initially disgusted by the filthiness of their house, but notices that they have taken special care of various memorabilia they have collected from all of their missions with her.

On the third night of the Grand Magic Games, Fairy Tail visits the popular water park Ryuzetsu Land to relax, meeting and playing with various other competitors from the tournament.

In a crossover with Rave Master, Natsu and his friends separately meet Haru Glory and his companions Elie, Plue, Musica, Let, Julia, and Griff. Natsu and Haru strike up an immediate friendship until Haru learns that Natsu is on a mission to capture someone at Ruby's casino who seemingly matches Elie's description. The two break into a destructive fight that is eventually broken up by Erza, the actual, unwitting target of Natsu's mission.