The boutique gives the dresses it sells names. Memi's dress is called the "shoumen kara iku wanpisu 正面からいくワンピース," the "going at things head-on dress".
The shop is in the Laforet fashion mall in Harajuku, Tokyo. Here is an image of the dress from their online catalogue:
The shop is part of the Stripe International company, and carries 70% vintage clothing and 30% new. This dress is new, and costs ¥11,340 ($106). It comes in blue, black and pink-beige. The blue and pink-beige are now both sold out.
The shop's "brand director," Akazawa Eru posted this tweet saying Memi had worn the dress in her final appearance as an idol and it both made her happy and was a great honour. She wished Memi happiness, and said she thought Memi must have been aware of the name. I think so, too, since "straight ahead" is how she addressed the reason for her leaving: that it was because of a stalker bothering her and her family.
In Akazawa-san's tweet, she posted a Direct Message she received from someone who said: "Yesterday, August 11, the idol I love most in the world retired from entertainment. She is Kakizaki Memi, formerly of Hinatazaka46. She hadn't appeared in public for several months. Unable to stand being stalked, she decided to graduate from being an idol, and after a long absence stood before her fans to give them a final word, as she left the entertainment stage.
In this last appearance, Memi-chan was wearing a blue dress that blended with the atmosphere. I didn't know the dress, but I knew at a glance that it was from Lebecca. Wrapped in blue, Memi-chan finally showed us her smiling face.
Lebecca's dresses support women by enwrapping them in a feminine consciousness. For me, as for anyone else, they are battle-dress. Please continue to make such dresses.
From the bottom of my heart, I am glad there was such armour for Memi to wear as she summoned up her strength to stand in front of her fans. I too bind myself in such armour to live through modern times!
I wanted to pass these thoughts on to you, and took this opportunity to do so. I apologize for the sudden DM. I will continue to support you from now on!!"
A reply to Akazawa-san's tweet by the same person included pictures of a Lebecca dress Memi had worn last autumn:
It is called "high-neck frill dress for gazing at the pre-dawn."
via Anakamirikarutenani