The title Kanreki Shonen
means 60-year-old boys. People’s sixtieth birthday has special importance in the Japanese tradition. It’s been said that the 60-year-old person is once again a baby who is entering the next 60-year cycle based on completing a full cycle of the zodiac with its 12 animal years 5 times. It is a rebirth. We call baby “akachan,” and “aka" means “red.” So those lucky enough to reach 60 receive the traditional red cap, red chanchanko vest, etc. Red color is also used as a talisman against evil.
Long story short, I painted the ground red because red is the key color to those who are 60 years old. I also thought that the red cover would stand out in the bookstore shelves.