Based on the setup in Cap 3, here is what the community expects for the next installment (scheduled for release in 2 weeks according to the author’s Twitter):

But this summer, something was different.

The wooden box is the McGuffin that drives the plot forward, but its true function is symbolic:

When searching for the newest ("new") subbed versions of Chapters 1, 2, and 3, viewers generally rely on specialized streaming platforms. Because this project is classified strictly as an adult OVA (Hentai) rather than a mainstream shounen or seinen broadcast, it is hosted on mainstream platforms like Crunchyroll or Netflix. To track updates safely:

They reached a door marked .

Ryuuki is introduced to the work of a popular adult film actress named (or Kirill-sama) by his friends.

As Kirill sticks around, the boundary between fan and partner blurs. This chapter focuses heavily on Ryuuki’s transition from a naive boy to someone experiencing the realities of adult relationships, matching the literal translation of the title.

The initial episodes of Shounen ga Otona ni Natta Natsu focus on the dismantling of Ryuuki's sheltered life and his introduction to a complex new relationship. Chapter/Cap 1: The New Normal

“The Second Summer Initiative,” said a voice behind them.