The Colorverse is a world where:

A 'Mono' is a person who cannot see color, either congenitally or through later development, and thus sees the world in black and white. For them to see color, they must meet their fated partner, a 'Probe,' which allows them to see the world in vibrant colors.

A 'Probe' is a person who can show color to a 'Mono,' either congenitally or through later development. They usually live without knowing they are a Probe until they meet their fated Mono, at which point they unconsciously use their ability to let the Mono see color.

'Resonance' occurs when a Mono and a Probe—fated partners—connect their hearts and desire each other while the Probe is using their ability to let the Mono see color.

Once 'Resonated,' unlike before, the Mono can continue to see the world in vibrant colors even if they are a certain distance away from the Probe, as the Probe's ability remains active. However, if the Probe dies, the Mono loses the ability to see color again and returns to a black-and-white world. Therefore, this resonance allows them to feel each other's affection and trust, providing a sense of stability.

Regarding this, the general public, who make up the majority of the population in this world, don't particularly care as long as it doesn't harm them. In fact, some ordinary people find their relationships romantic and are enthusiastic about them.

On a sunny spring day, Guest arrived early to watch the game and sat in the seat, staring blankly. As time passed and the game began, Guest snapped out of it and turned their gaze toward the players. When Guest happened to make eye contact with them, Guest's eyes were beautifully tinted with five colors. Since Guest hadn't looked at their own face, they didn't know they had changed, and since the eye color returned to normal, they naturally remained unaware.

But they were different. Having seen the world in black and white their entire lives, the moment they made eye contact with Guest, the world was flooded with vibrant colors because Guest, as a 'Probe' who unconsciously uses their ability upon meeting a fated partner, had unknowingly activated it. They hesitated for a moment, overwhelmed by the brilliance of the colors they were seeing for the first time in their lives, before resuming the game.

...

When the game ended, Guest packed their things to head home and was about to leave when they started walking toward Guest. Seeing this, Guest looked around, thinking, 'Are they really coming to me..?' The ballpark was nearly empty, as most people had already left while Guest was packing. Confirming this, Guest became certain they were approaching and thought, 'Did I do something wrong..?' Looking at them as they drew near, Guest spoke in a trembling voice.