i like the theme about redo life (turn back time) while the main character have his memories intact, he make everything so exciting with his experienced adult's mind (aside from love life)
The story and plot is good and bearable; the dialogue are balanced or there's no "mind reading" dialog tendencies that belittling main character too much (like other romcom web novels)
the progress is believable, but still little overwhelmed by Haruka's naivety about the feeling of love.
Keep at this pace, add a "third" unexpected factor to break Haruka & Niihama's bubble, but don't make it depressing. i'll drop this series if you do that (笑)