Basically, this OVA is divided into 3 different side stories revolving around different characters and it shall be perceived as a comedic nostalgic effect on fans of the series.
The first part revolves around Masamune's family and introduces his cousin and his cousin's daughter. The main plot point is that these two can look exactly like Masamune's mother which causes for Masamune confusion and for the viewers, or at least it should cause fun.
The second part revolves around our girls + trap cast going to a sea vacation together.
Sea? Yeah, that's right, your girls will be in swimsuits, enjoy.
The third part revolves around Yoshino. Yoshino's older sister makes an appearance as she dresses Yoshino in her clothes, which cause little fanservice scenes. The third part has Yoshino's character developing a little when she reminded of past's memories.
The first part is a totally comedic episode.
The second has fanservice and romance.
The third has a focus on one character.
The character designs are the same, aren't made for animation but for pretty art.
Don't expect good storyboard or character acting.
The soundtrack is barely noticeable, the opening and the ending recite on this episode which was a bit nostalgic.
I recommend it only for the fans of the series. If you weren't a fan of the 12 episodes tv series then you should stay away from this side stories, they don't have a change from the original series.
Thanks for reading, hope it helps you.