Swimming Pool & Happening Time

 is the third special chapter of the Seven Magicians series, initially released in Trinity Seven: 7-Nin no Mahoutsukai 3 volume on February 27, 2015 and later compiled in volume 15.5 on January 7, 2017.

Summary
While swimming alone in a pool while recovering her magic, Mira is interrupted by Akio who comments that her usage of the water as an alternate for her crystal ball resembles the concept of Arata's magic, much to the Superbia's magus' displeasure.

Nevertheless, the two continue to the showers where Akio notices Mira's insecurities over her figure which she recounts her own experience before transforming into her younger self as a demonstration. However, upon being questioned by her sudden interest in her appearance, Mira denies the notion that Arata is involved to the former Spriggan's amusement.

Afterwards, Akio notes the positive change of several members of Trinity Seven due to Arata's influence, but nevertheless promises to support Mira's decision. As such, the Head of Grimoire Security declares that she will not accept the Demon Lord Candidate until Arata himself unexpectedly appears. Yui quickly arrives to apologize for directing him towards the girls bathroom before attempting to leave so they can change together much to Mira's chagrin. But as the Trinity Seven of Superbia prepares to dispatch Arata, her towel suddenly falls down to reveal her full body in front of him. While Mira is frozen with embarrassment, Yui comments that her bust has grown before the furious lady finally lashes out and strikes Arata with her grimoire. A pool of blood forms around the victim as the trio of Trinity Seven watch, particularly Yui who becomes concerned over his injuries.

Characters

 * Mira Yamana
 * Akio Fudo
 * Arata Kasuga
 * Yui Kurata

Flashback

 * Lilith Asami
 * Levi Kazama
 * Selina Sherlock
 * Arin Kannazuki

Trivia

 * Akio recalls Arata's rescue of Yui while noting that eliminating her was the only course of action Grimoire Security could follow, referring to the events from Labryinth & Ninja to Magic Gunner & Shooting.