Most of what Reborn knew about Hyper Intuition was the fruit of heavy research into Primo's life, his personal notes, the testimony of his contemporaries and the legends which sprang up in his wake. Apparently, the Bosses after him had not possessed it as powerfully, or controlled it as deeply; their techniques and thoughts on their powers, if they felt it safe to pass such information on, were never quite as comprehensive as Giotto's and painted a much paler picture.
Timoteo was more willing to talk about his powers and experience - to Reborn, at least - and he agreed: Giotto had most likely experienced the world in a completely different way from normal people. At the very least, everything under the sun must have been vastly more intense. At most... well, maybe they simply couldn't comprehend it.
Sawada Tsunayoshi possessed Hyper Intuition. That was a fact. Reborn may have doubted it for, oh, thirty minutes or so into their first meeting, but the more he watched the boy, the clearer were the signs.
Sawada Tsunayoshi suffered from Hyper Intuition. He carried it like it was a disability, and like the disabled, had learned to cope as best as he could.
Hyper Intuition is a form of hyper awareness. Even when out of the trance-like state of his Dying Will, Giotto was capable of detecting the most minute changes in a person's expression--
the minute dilating of pupils, the slight pulsing of muscles in the vicinity of a concealed vein, a light sheen of sweat when it was unexpected and the lack of it when not so, the tell-tale signs of lies, of fear, of lust
--and in the ambient around him--
a single smell amongst a sea of different smells, a change in air currents caused by a pair of feet blocking the space beneath a door, the pressure of a concealed enemy's stare
--not out of experience or training, but as a simple matter of fact. He only ever noticed his observation skills were unusual thanks to his friend G, who took stock of their different skills and limitations. Giotto had called it Intuition at first because he had no other way of explaining why he could so easily see through liars and foretell the weather; G had jokingly re-dubbed it Hyper Intuition because intuition alone couldn't possibly justify such near prophetic abilities. It was only many years later that Giotto was able to pinpoint the signs he'd taken for granted his whole life, likely thanks to years of battling among experienced assassins and hardened soldiers, who'd teach - or brag - about all the little learned cues which helped keep them alive.
Late among his notes, Giotto had described himself as lucky for achieving the Dying Will State, for his heightened awareness was “very tiring at times” and his Dying Will allowed him to concentrate and "block out the noises". Some of the Family's historians had wondered whether Primo had, later in his known life, suffered from hallucinations or some sort of encroaching insanity which he could unconsciously overcome through his Dying Will - but Reborn had known the truth from long hours of silent vigil, gun in hand, even before he was ever told of this theory.
The world is awfully noisy. Period.
What would the world be like, for a baby to whom the rubbery gloves of the doctor felt only too stark, the birthing slap too sharp, the efficient bustling of nurses and rubbing of cloth too loud? The milk from his mother's breast indescribably sweet, the warmth of her arms overwhelming? For Reborn, who had recently suffered through his second babyhood, the initial intensity of all senses was very clear in his memory - and yet, his awareness was still just the sharpened awareness of the best hit-man in the world, not Giotto's superhuman awareness.
For Tsuna, who might be the closest the world would ever get to Giotto again, growing up under the modern world's constant sensory bombardment must have been nearly insanity-inducing.
The teacher drones on, wrinkles stretching and deepening and loose skin wobbling around his mouth, while outside each falling raindrop hits the window and the ground outside with a wet smack, each perfectly distinguishable from the other by size and surface. Many pencils of differing hardness scratch papers of differing textures, their sound underscoring the constant bickering and giggling and hissing whispers of bored children. The teacher's pinkish red marker squeaks onto the stained, scratched, barely reflective surface of the whiteboard, leaving behind minute traces of felt as the ink dries and solidifies, slowly losing its wet sheen. On the next room over, some other teacher's marker is also squeaking while their voice alsodrones on and the children also hiss and whisper. Far away in the background, cars honk and splash on the wet street. Someone kicks boredly at the leg of their own chair. Sweat lingers in the air, pressing from all sides. Someone farts. The smell mixes with the cloying mintness of someone else's eucalyptus drop. Someone is surreptitiously chewing gum; the teacher doesn't notice, but...
...from very early on, Tsuna must have had to force himself to ignore nearly all the information around him. And he’d learned to do it so thoroughly and competently that he became unable to focus on anything relevant. He'd developed some sort of homegrown ADD as a protective measure. That much seemed clear.
Sometimes, Reborn wondered if Tsuna’s usual high-strung reaction to any unexpected situation, dangerous or otherwise, actually involved a heightened response from his senses. When he grabbed his head and squeaked loudly, was he begging for the noises to fade back away? Was that his way of muffling his ears and singing loudly at the world? Or was it just the sight of an exploded bedroom?
Having reached his own conclusions, Reborn decided to concentrate on putting demands on Tsuna's senses. The initial Dying Will State would train his body to withstand Hyper Dying Will; in parallel, he pushed the kid into all sorts of absurd situations in order to trigger his senses as often and as hard as possible. But except for consistently spotting through his disguises, Tsuna stubbornly refused to show progress.
But eventually, Leon produced the Rebuke Bullet, right when it was needed the most. And Reborn had the pleasure of watching, front seat, as Tsuna first showed control over his body and senses - stunted as they must have been after going unused for so long - and, most important of all, he seemed able to filter out all the noise.
He was a sight to behold.