The day they met and tried to kill each other, Shizuo chased him throughout Ikebukuro, Izaya stopping once in a while and slashing at the protozoan to remind him that he was not an opponent he could intimidate. Unlike the others who had gone against the blond, he was not weak. In fact, Shizuo should've known better than to piss off Orihara Izaya, because now Izaya would have to tear the idiot's life to shreds as retribution for breaking his heart. He would continuously ruin the monster's life until the day he got bored of toying with the clearly inferior creature that had the audacity to reject him without even giving him a chance.
He never forgot to smirk throughout the chase even though his heart kept on shattering into smaller pieces the longer it lasted, every step he took while running away from Shizuo strengthening his belief that the blond was not above humans, but below them. Shizuo was clearly a dumb monster that Izaya could not afford to love, so he'd have no choice but to push back the strong feelings his broken heart had been incapable of tossing away the second he got acquainted with the real Heiwajima Shizuo. He would have to work hard on suppressing this inconvenient love until nothing would be left inside his heart besides hatred and disdain when it came to the monster who'd hated him from hello.
Unlike the brute following him, Izaya always paid attention to his surroundings, especially when crossing the street as to avoid getting hit by a car. He knew exactly which direction to take and how fast to run, and even though his expectations of Shizuo had plummeted into the abyss earlier that day, he was still shocked to hear the sounds of a horn going off and of a body being hit, followed by a grunt of pain coming from the blond. For a second, when he realized what'd just happened (how could anyone be so careless?), he froze in his tracks, heart hammering wildly inside his chest as the thought of Shizuo dying speared through his mind.
The deafening silence didn't last for long though, and it was followed by a gasp and heavy breathing coming from the fallen brute. The pain in his chest lessened when he saw the blond stirring on the ground, but his lips curled into a sneer before it switched to a smirk and he approached the driver who appeared to be frantic over hitting someone.
"It's okay. It's okay," he assured him as he retrieved his wallet from the back pocket. "He's built tough," he then added as he pulled out a few bills.
"Is he really alright?" the man stuttered, worried that he might end up in prison.
"It's fine. It's fine," Izaya insisted as he handed him some money. "Good work."
Leaving Shizuo to writhe like a worm in the middle of the street (not that he actually was, but Izaya would've liked to see it happen), he headed towards Shinra's apartment on legs that felt like cotton. It wasn't that he'd been scared (the thought alone made him sneer), but the whole thing had been emotionally taxing and he couldn't wait to get his injuries treated, go home, take a shower and jump into bed, the only place where he would finally allow himself the privilege of crumbling to pieces if only for a night.
Because he was smiling as he walked down the street, nothing looked amiss to the people passing him by, but maintaining the facade was proving to be harder than anticipated and he doubted his mask would last for much longer at the pace he could feel the fissures appearing, manifesting on the outside through a twitching eye or a quivering hand. He wished he could go back and tear out the monstrous heart that didn't resonate with his own, to make Shizuo feel the agony of having it crushed by someone else, but he couldn't. He shouldn't. In the end, he didn't.
Shinra received him with that idiotic smile on his face, and Izaya returned it with a smirk, hoping that the bubbling idiot couldn't read him well enough to see what was going on in his heart. Even if Shinra suspected something, Izaya had no intention of ever confirming it for him.
He didn't really think that his friend would betray him, but he couldn't risk it. Shinra already knew too much about him, and Izaya didn't like the idea of others possessing information which could be used against him.
"Interesting," Shinra chirped as he started disinfecting the abrasions on Izaya's right hand. "What happened here?"
Izaya shrugged, not really caring to answer.
"Don't tell me that Shizuo-kun caught you!" Shinra gasped, but his eyes were twinkling with amusement and it irritated Izaya.
It wasn't easy, considering how heartbroken he felt on the inside, but he swallowed the insults he was one step away from spewing and instead chose to answer calmly. "I took a tight turn and scrapped my hand against the—"
There was a loud noise coming from the hallway and Shinra momentarily abandoned his task to go see what was happening.
"Oh, what a coincidence! Izaya's here too!"
Judging by the beastly grunts, the uninvited guest was Shizuo, who had either come there to get medical attention or to beat Shinra to a bloody pulp for thinking that introducing him to Izaya was a good idea. Celty was trying to calm him down, but Shizuo had ripped the door from its hinges and was obviously planning to use it as a weapon against Izaya or against both of them.
It was much too soon to face Shizuo again, but Izaya still locked eyes with the blond, his usual expression back into place. "More importantly, why aren't you hurt?" It was a valid question, considering the brute had just been hit by a truck, but one he expected no answer to.
"Kill! Kill! Kill!" Shizuo started as he raised the door to hit Izaya in the head with it, but Celty moved in between them, trying to calm him down before things escaladed and someone got hurt.
Running away was out of the question, for Izaya was no coward, so he waited until Shinra had finished bandaging his hand before he got up and walked out of the apartment, leaving behind a fuming Shizuo who was surprisingly no longer bleeding from the cut on his chest.
Izaya didn't remember much of what happened on his way home, thoughts of Shizuo irradiating him, melting the grey matter of his brain and leaving him unable to think clearly. Shizuo was like poison, tainting his heart and affecting his brain. He mostly stumbled into his room, one hand gripping the red t-shirt as he collapsed on the bed, the mental and physical exhaustion finally taking their toll.
It took him half an hour to find the strength to get up, undress and take a shower, the desperate need to get rid of the dust and sweat covering his body after running for so many hours pushing his limbs into motion even though he wanted nothing more than to curl into a tight ball and hopefully fall asleep. His brain needed a reboot more than it needed food, so when he got out of the shower, with bloodshot and red-rimmed eyes, it wasn't because he'd been crying, but simply because he was sleepy. His face wasn't slick with tears, no; it had merely been the hot water beating down on him. Surely, he would never cry over a stupid monster, one unworthy of the attention and affection he'd tried to bestow upon it.
That night, after much tossing and turning in his bed, he finally fell asleep, light brown eyes haunting his dreams and turning them into nightmares as Izaya relived the rejection he'd experienced earlier that day. When he woke up, he thirsted for blood, and the first thing he did after grabbing something to eat (after all, he needed his strength), was to sic some of his game pieces on Shizuo.
And so it went on for years, their enmity growing in intensity until their deep hatred for one another became known throughout the city and people started referring to Shizuo as Ikebukuro's strongest while Izaya became the daredevil the monster seemed incapable of catching.
With every insult, every fist swung at him and every vending machine thrown in his direction, Izaya's love for Shizuo died a little more, as did the informant's admiration for that strength which he came to despise. Shizuo was an unpredictable beast, that disproportionate strength often used to throw a wrench into his plans whenever he'd run into the protozoan who was under the erroneous impression that Ikebukuro belonged to him and him only. It didn't, and it never would; that was a fact.
