The title, The Days of Diamond, speaks volumes about the story. In Japanese, the title is The Merits and Demerits of Diamond (Diamond no Kōzai, ダイヤモンドの功罪). Japanese Title portrays both the bright and dark sides that come with a gleaming, fully polished diamond, not its raw form. On the other hand, The Days of Diamond can be interpreted as the ordinary days in the life of a "diamond" (a genius). The singular form of "diamond" conveys a sense of loneliness.

The title is remarkably fitting. Those born with superior physical abilities excel in any sport. But what sins could a physical prodigy carry?

Youth sports are divided by grade levels. This division is cruel. Think of soccer, basketball, or baseball. A mere month’s difference in birth date can put you in a different grade. Some kids in the same grade might be born a full 12 months apart.

The difference in growth over a year is monumental for children.

Still, in a sense, this division is rational, so we accept it. But what happens when a once-in-a-decade sports genius appears?

In soccer, there are 11 regular starters. Basketball has six. Baseball has nine. If you’re a pitcher, maybe only one. To make it to the pros, you must perform in tournaments.

So what do you think?

The Days of Diamond (manga) Synopsis

Jiro Ayasegawa, a fifth grader, is blessed with extraordinary athletic talent. His body is far larger than those of his peers, and he instinctively understands how to move it skillfully. When he tries swimming, he immediately masters it within a day or two.

But a genius stands alone.

Some kids lose because of him.
Some kids give up their dreams because of him.

Adults become obsessed with Ayasegawa, their eyes alight with ambition, and children not only face defeat but also suffer emotional scars in the face of his overwhelming talent.

Ayasegawa enjoyed his time playing baseball with his teammates, but his talent began to disturb the adults.

Yasu’s father, one of the team members’ parents, began paying special attention to Jirō. Meanwhile, the Bambies’ coach secretly filmed Jirō’s pitching and sent the footage to the U12 national team selection committee.

The Days of Diamond (manga) Character

Jiro Ayasegawa
The protagonist at the center of the story. Despite being only a fifth grader, he stands over 169 cm tall and possesses overwhelming athletic talent in any sport he tries. His very presence impacts not only his classmates but also adults, leaving them unsettled.

Iga / Haruyuki Igarashi
The Bambies’ catcher and Jirō’s teammate. Though he can’t catch Jirō’s fastest pitches, he was the one who inspired Jirō to start playing baseball. He attends a different school, Keiyō Yōchisha. Unlike Jirō, Iga understands the importance of enjoying the game with his team, making him a kind-hearted boy.

Yasu / Yuki Yasuda
A fifth-grade member of the Bambies who attends a different school than Jirō. He carries high expectations from his father, a former semi-pro baseball player.

The Bambies’ Coach
The coach of Adachi Bambies, who leads the team with deep affection and sincerity for the children. However, captivated by Jirō’s extraordinary talent, he sends a video of Jirō’s pitching to the U12 selection committee without Jirō’s consent, which greatly impacts the storyline.

Yasu’s Father / Yasuda
A former ace pitcher for Nittō Gas, a powerhouse corporate team. While he subjects his son to rigorous baseball training, he becomes deeply shaken after witnessing Jirō’s raw talent.

Tougo Hina
Despite his rough demeanor, his exceptional physique and talent earn him the position of lead catcher and cleanup hitter for the U12 national team. He plays for the Neyagawa Fighters alongside his childhood friend Madoka. Tōgo holds great trust in Madoka, and this puts him at odds with Ayasegawa, who unknowingly insulted Madoka by not realizing the extent of his own talent.

Madoka Tomoe
A pitcher with both skill and exceptional leadership, Madoka is a mood-maker for the Neyagawa Fighters and supports the team as the second-string pitcher for U12. His strong bond with his childhood friend Tōgo adds depth to the story.

The Days of Diamond (manga) Review

While there are many baseball mangas, The Merits and Demerits of Diamond tackles themes distinct from the rest. It vividly depicts the shifts in behavior among a genius, their peers, and the adults affected by this genius.

That said, the artwork is approachable for all readers, and the composition and pacing of the panels make for a dynamic read. The panel usage and camera angles build a sense of tension and anxiety, only to return to a comforting sense of normalcy, keeping readers engaged throughout.

The portrayal of the emotional distance between the genius and the people around him, which never seems to close, is masterfully done.
If the protagonist were merely a blessed athlete excelling in his sport, the story would be simpler. If he had the ambition to be the best, it might even be easier for readers to digest.

But Jiro Ayasegawa simply wants to enjoy sports, yet consistently outperforms everyone. Watching his friends, who are serious about their sports, get hurt by his unintentional dominance, he repeatedly quits.

Jirō doesn’t consider himself gifted, nor does he understand why his peers "can't" do what he can.

This, in essence, is Jirō’s “sin.”

He picks up the technique of throwing a curveball just by watching a video—without realizing how remarkable that is. Because it comes so easily to him, he doesn’t understand why others struggle.

Jirō simply wants to have fun with his friends, so he doesn’t grasp the mindset of those who want to win in sports, leading to a complete communication breakdown.
But outside of sports, he’s just a normal 11-year-old boy. There’s even an extra manga at the end of the volumes showing him spending time with friends, reminding readers that Jirō is still just a regular kid.

Let’s explore Jiro from four perspectives.

First, his family. He comes from a single-parent household with three sisters, and while not wealthy, he is very relaxed at home, behaving like any normal 11-year-old.

Next, his team, the Bambies—a small, weak team focused on fun. He grows close to Yasu and Iga. They lack the drive to be the best, which allows Jirō to play baseball in peace. However, the catcher can’t handle his pitches, so Jirō never throws at full strength, nor does he play in games. The adults recognize his talent, complicating his relationships with Yasu and Iga.

What about the national team? There’s a catcher who can handle Jirō’s full strength. But even here, Jirō’s overwhelming talent creates distance.

Jiro can throw a perfect game, but the batters can’t score, and they feel guilty. Catcher Tōgo can catch Jirō’s pitches, but his hands won’t last much longer.

The emotions between Jirō and his teammates are completely misaligned. In fact, they might have preferred Jirō to be an arrogant genius.

The adults are the ones who get obsessed. The Bambies’ coach, who said fun was the priority, submits Jirō’s footage to the national team selection without permission. Yasu’s father starts to place his hopes in Jirō instead of his own son. Even the national team coaches struggle with how to handle him.

How will Jiro Ayasegawa grow, and what role will baseball play in his life?

In the opening of chapter 4 in volume 1, we see Ayasegawa as a high school student on the mound. He silently whispers, “I want to play baseball with this team forever.” The score is 0-0, bottom of the 12th inning. His high school has hits but no runs. The opposing team hasn’t managed a single hit off Jiro.

Let’s keep an eye on how Jiro’s story unfolds, as he continues to play baseball, at least through high school.

The Days of Diamond (manga) Author

Ohashi Hirai
In 2023, the baseball manga The Merits and Demerits of Diamond began its serialization in Shueisha’s Weekly Young Jump. The series earned the top spot in the "This Manga is Amazing! 2024" (Male Category) and placed fifth in the "Manga Taisho 2024" awards.