The famous sestet of Teikō Junior High are renowned basketball prodigies that only burned brighter as time went on, they are known as the "Generation of Miracles". The team have had an interesting progression (or regression, some might argue) as their talents became more refined.
Basketball is a team sport, and Teikō's Generation of Miracles reached a point where the notion of sportsmanship and teamwork were thrown out the window in the name of victory; and they had plenty of victory. The team's ideologies on winning were the reason Tetsuya Kuroko distanced himself from them, as the love for basketball no longer drove the team. Gone was team spirit, and a tense isolated attitude was born among the players.
Who Are the Generation of Miracles?
The Generation of Miracles consists of six people: Ryōta Kise, Shintarō Midorima, Daiki Aomine, Atsushi Murasakibara, Seijūrō Akashi and the phantom sixth man Tetsuya Kuroko. Each of these players possess their own unique talent on the court. Kise's famous moves are copycat techniques, where he can mimic any of his opponents' moves and use it against them. Midorima is an expert shooter, with his range spanning the entire court. Aomine was Teikō's Ace player, with passing, scoring and speed abilities that are way above average for someone his age. Murasakibara uses his hulking size to execute powerful (mostly) defensive strategies. Akashi's deadly Emperor Eye ability predicts every move his opponents make. Kuroko excels in various passes and misdirection, and is dubbed the team's "shadow" or "phantom".
The Formation of the Team
When the current Generation of Miracles were first years at Teikō, they all joined basketball tryouts. The organizer of the club informed the boys that Teikō take their basketball very seriously. After the tryouts, the team strings were announced. Up till this point, no first year ever makes the first string. While Kuroko managed to secure a spot on the third string, Midorima, Aomine, Murasakibara and Akashi became first-string players, much to everyone's shock. It was established on day one that these four were something special.
Kuroko & Aomine
To avoid crowded gyms, Aomine decided to practice in the third string gymnasium. It was here where he met Kuroko for the first time while he was practicing after hours (despite thinking he was a ghost that haunted the gym, at first). Kuroko has been practicing in the hope of making at least the second string. After conversing for a bit, it turns out that Kuroko and Aomine have the same love for basketball despite their differences in demeanour and skill level in the sport. Even though they are in different strings, Aomine's logic was that anyone who loves basketball cannot be a bad person; by that logic Kuroko is the best person in the world.
They practiced every night together, and developed a friendship. They even hoped to play on the same court together, some time. In tough moments when Kuroko contemplated quitting basketball because he wasn't advancing, Aomine convinced him not to because his drive and ambition is inspiring.
"You have almost no presence for others... this is what makes you special"
The rest of the Miracles walk in on Kuroko and Aomine practicing in the third string gym. Akashi is instantly curious about Aomine's new practice buddy. Akashi sees something in Kuroko, ironically a person no one ever sees. His distinct lack of presence comes off as an insult, but Akashi assured Kuroko that is can be a great advantage. He notes that Kuroko's constant practicing is not fruitless, as he can tell that he has gained experience and skill even if it is unnoticeable.
Akashi saw potential in Kuroko and extended a few tests to him to realize it. A few months later, Kuroko figured out how to use his diminishing presence to be a force of nature on the basketball court. Kuroko exceeded expectations on Akashi's challenge to use his "invisibility" as a strength. Subsequently, Kuroko was promoted to first string.
Introducing Kise
Now that the first string team are second years, Kise has now joined the second string team and was quickly promoted to the first string. Under Kuroko's mentorship, the "Generation of Miracles" was now complete and as we know it today. Akashi at this point is now the vice-captain, and has already made changes to the team, such as telling Shōgo Haizaki that he should step down as starter so Kise can replace him with his superior talent.
Changes Emerge
With the whole team assembled, the Miracles individual abilities have been getting stronger by the day. Winning was as easy as breathing for them. They were feeling like basketball was not challenging anymore and became comfortable with victory, which they always got. Aomine in particular has been dubbed a "Monster" because of how much he grew in power. He began skipping practice because he believes that his opponents won't try to beat him if he's too powerful. The new coach Sanada also had trouble managing him during practice until he eventually let him come and go as he pleased. Akashi is also now the captain of the first string. When Murasakibara wanted the same privileges as Aomine, Akashi decided to settle this in a basketball game. His Emperor Eye ability was born and so was his second persona, one who was more cruel and intense. Despite losing this game, Akashi allowed Murasakibara and the others to skip practices as they wish. He felt that practicing would be only stain the victorious team they had, they clearly had no need for sportsmanship.
The team was crumbling. While the victories were secured, the teamwork was missing. Each player played by himself, the bonds they formed broken. Under these new rules and mindset, the Generation of Miracles were no longer a team, but a collection of talented a players. They were too comfortable with winning, to the point where they would score for the other team just to keep the game interesting for them. Kuroko rejected this way of playing and quit the team before their last national tournament. No one has smiled while they played anymore, teamwork was non-existent.
When they graduated middle school, the remaining Miracles developled a well-recognized disdain for each other. As they parted ways, they vowed to face each other in basketball at their respective high schools. Their distaste for each other was evident as they continued to play against one another at the various tournaments throughout the anime, as promised.
A New Bond is Formed
As each of the Miracles' high school teams were defeated by Seirin High, a different kind of relationship has been blooming between these former teammates. They began attending each other's games as spectators and even encouraged Kuroko in the Seirin vs Rakuzan match in the final season. In the last episode, the Generation of Miracles were seen playing basketball together on Kuroko's birthday and celebrated with him alongside his Seirin team. Being the first defiant Miracle, Kuroko was instrumental in reuniting the team he cares so much for.