If you could connect the past and the future with your smartphone, how would you fix your regrets?
The summer of high school second year―the girls are more whimsical, more mysterious, and more beautiful than ever.
The feeling of first love, the bittersweet memories of our high school lives, a regret-filled summer.

Summer, 25 years old―I became a salaryman before I’d realized. Looking up to the sky, I remembered the dreamy days. Reminiscently, I turned on the smartphone I used during my high school days. I opened the messaging app and sent myself a message.
“You will regret it”
A message to my past self. A message that cannot be delivered. But — the phone responded.
“What is this, all of the sudden?”
This is — a message from myself — from the past.

[From tone work's official site. Translated by Silvwy.]