Me, My Girlfriend, and Sparklers

I grew up in the village with my sister, Natsuka Koike, who is two years older than me.
I thought I could be with my strong and kind sister in this village for a long time to come....

Until "that summer"...

And now, in the present day... Yu Tanaka, the main character who experienced "that summer" 13 years ago, is in a weakened state.
When he thinks of Natsuka Koike, he cannot resist the feeling of ejaculation.
In order to suppress his regret after masturbation, he decided to sleep.

When he wakes up, he finds himself in "that summer" 13 years ago.