Meguru Ueno, Hajimete no Gal manga's author, posted photos of the manga's 5th volume on Twitter.
There are two versions available, a regular version and a limited version with Original Anime BD.
The regular version's wraparound says
"Do you want to 〇〇 on our trip? Fine, you can do more...♡"
"Can I step up the stairs to be an adult?!!!"
and announces that the manga has sold over 600,000 copies.
The volume will be released on December 26th, 2017.

『はじめてのギャル』五巻の献本届きました！今回はオリジナルアニメBD付き限定版も同時発売（要予約）12/26発売ですよ〜よろしくお願いします！✨(о´∀`о)
はじめてのギャル (5) (角川コミックス・エース) KADOKAWA https://t.co/1IqnjLoV9V @amazonJPさんから pic.twitter.com/iVMVcBODB1

— 植野メグル@はじギャル5巻12/26発売！ (@uenotei) December 15, 2017

12/26発売はじギャル五巻の店舗特典まとめました〜！！なくなり次第終了ですのでお早めによろしくお願い致します☺️✨ pic.twitter.com/C4GPgfY08x

— 植野メグル@はじギャル5巻12/26発売！ (@uenotei) December 18, 2017

Hajimete no Gal, aka My First Girlfriend Is a Gal, written and illustrated by Meguru Ueno is an ecchi-comedy anime.
The manga has been serialized in Monthly Shonen Ace.
It inspired TV anime which was aired from July to September 2017 with 10 episodes.

Via - Official Twitter Account:
https://twitter.com/uenotei/status/941604033298538497
https://twitter.com/uenotei/status/942648410644946944

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