Chapter Text
The idea has been sitting in the back of Illumi's mind for a while now but it isn't until two months after he'd told Killua that he'd leave him and Alluka be that the feels like the time is right.
Having separated himself from Gon, Killua has spent most of his time in the passing weeks moving from town to town trying to avoid Illumi's attention. The fact that he didn't trust Illumi to stay true to his word and avoid them would be a little insulting if he hadn't been tracking them on and off during their time apart. What makes the day that Illumi decides he needs to act different from the previous days he's been following them is that Killua's phone rings and, rather than answering it, he mutes it with a sad smile and goes back to eating dinner with Alluka.
As perceptive as Killua typically is he doesn't notice that Alluka is paying attention to the moment. But Illumi sees it from where he's sitting on the opposite side of the diner. He sees her face drop and then her smile return just as quickly, big and unnatural when Killua looks up at her. Illumi can tell that for the rest of the evening she's only pretending to happy and upbeat the way she normally is. She's probably assumed, like Illumi has, that the phone call was from Gon, and that he was ignoring it because he didn't want to distract himself from looking after her.
Later, when the two of them are walking back to their hotel room, Alluka asks him if he meant it when he said that they'd be together forever.
"Of course I did. I promised didn't I?" Killua says, squeezing her hand. Alluka squeezes it back but even Illumi can tell her smile is forced.
Small and delicate as the moment is, it's leverage for someone like Illumi, and all that he needs to pry open a chasm.
***
You're holding Killua back by being around him Illumi tells the needle. Two blocks down he can vaguely sense Killua and Alluka's presence heading in his direction, their pace quicker than he'd prefer. He stays still in the crowd, concealing his own presence as best he can while inflicting intent into the needle If it weren't for you he'd be with his best friend. He hates you. Why wouldn't he? You need to leave him. You need to go home.
Neither Alluka nor Killua recognize him as they pass him in the crowd. Not only does Killua seem distracted by his attempt to playfully chase after Alluka but Illumi is wearing the face of an older man and the street is very crowded. With little effort he bumps into Alluka, letting the needle slide painlessly through the skin of her temple. She doesn't react. Her eyes are still focused back on Killua as she leads the two of them through the crowd and Illumi leaves the two of them, waiting for his needle to do its job.
The needle's work is powerful enough that in the few hours after it goes in there's a slow but noticeable drop in Alluka's mood. While she's still smiling, still joking with Killua and trying to look happy it's easy to see that there something bothering her. Illumi listens as Killua questions her, asking if she feels alright. She protests that she is but in the middle of dinner she asks Killua if they can head back to the hotel and they leave.
***
It goes on like this in every one of their interactions. Alluka is preoccupied and unsure in a way that Illumi has never seen her. It's weird how well a thing like her can mimic complicated human emotions.
***
Three days later Illumi watches Alluka step out onto the balcony of her and Killua's hotel. It's past midnight so it's possible that Killua is actually asleep and Alluka moves quietly, sitting down on the concrete. While Illumi watches from the roof of the hotel across from her Alluka pulls a cell phone out of her pink pajama pants.
Ilumi waits patiently as his phone rings, watching Alluka's small look of discomfort morph into mild panic before he answers on the last ring.
"This is Illumi."
"Illu-nii," Alluka says quietly, staring down at the road beneath her.
"Ah, Alluka," Illumi says. "What a surprise."
"I know." She sounds on the verge of crying but she keeps her voice quiet. "I wanted to ask for a favor if you're still following me and Killua-Oniichan."
"I might be. What do you need?"
"Could you," she turns back to stare in the hotel room. Illumi can hear her swallow over the phone. "Could you take me home please?"
Illumi counts to five in his head and then answers. "Of course Alluka. You should be with the rest of the family."
"Really?" Alluka says, her voice brightening slightly.
"Yes," Illumi says. "But I have a condition."
"Illumi," Nanika says. "Gimme your left hand."
Illumi looks down at a pair of large blue eyes and thinks. Getting Alluka out of her room hadn't been difficult. Killua-Oniichan hasn't been sleeping well, Alluka had explained to him over the phone, but he had been sleeping deeply when he actually did sleep. The larger problem for the evening was figuring out how to fulfill Nanika's requests.
"Did you want me to cut my hand off and give it to you or will holding your hand be good enough?" Nanika continues to hold out her hand patiently and Illumi figures he might as well try the less permanent option first. He takes her right hand with his left.
"Illumi, give me your right hand."
"Oh good, that's pretty easy then." Illumi takes her other hand.
"Illumi, pick me up."
By the time he's put Nanika down her eyes are black. He notices that she isn't smiling like she usually is.
“I want you to go home,” he says. “But once you get there you can't ever leave. Even if Killua tells you to."
Nanika's dark eyes turn downwards for a moment and then she nods. “Okay.”
***
Illumi doesn't catch his expression but he feels the rush of fear that leaves Killua when he wakes up alone in his hotel room. The feeling of it is warm and comforting to Illumi and he lets himself bask in its familiarity. There isn't much Killua can at this point after all so his fear is very much warranted.
Though he must know that there's only one person who knows where Alluka is, Killua is stubborn and for days he overturns nearly every inch of the town looking for her in a panicked rage. He picks a few fights, pays off a few different people only to get false leads and calls half of his contact list asking if they've seen Alluka. He knows it's futile and it's doing nothing to get him back to Alluka. He just doesn't want to face the truth.
Eventually Illumi sees his resistance give way and on the evening of the fourth day Killua takes out his phone. Before he even starts dialing Illumi knows he's won.
After the first ring Illumi stops concealing his aura and drops down from the rooftop he was sitting on, cell phone in hand. Killua looks at him with no small amount of bloodlust in his aura, his ringing phone still pressed to his ear.
"Of course it was you," Killua says. He hangs up, shattering the phone's screen. Illumi doesn't bother answering him. “Where is she?”
“Home safe.” He leaves the where you should be unsaid. “I'll be heading back myself soon to check on things. You can call Tsubone if you don't believe me - "
"No way. I'm going to see her myself."
"Are you sure Killu?" Illumi asks. "Alluka won't exactly be in any danger."
"You can stop it already. You've won okay? I'm going home."
For all that people insist on telling him otherwise, Illumi has always thought that he was a very expressive person and it's with a moment of internal struggle that he keeps his reaction down to a small smile and a pat on Killua's head.
"Of course I win. Come on, our ride is waiting outside town."
Killua doesn't bother going back to his hotel room to pack anything. Milluki had told him years earlier that when he left home for the first time he'd had nothing with him. If he's coming back the same way it's almost like he was never gone at all.
Barely an hour has passed by the time they find their ride and though Killua lets him lead the two of them away from town he doesn't look at Illumi during the walk. It's been years since he's ridden in a car with Killua - really done anything apart from offering him vague threats so the sudden loss of violent intent between them, or at least reciprocated violent intent, is new and strange. Killua takes the seat across from him in the limo and turns on his side so he isn't looking at Illumi. It's a cute, if very childish gesture. Since he's already won Illumi doesn't mind allowing it.
From having followed him and Alluka around for months he knows that Killua has barely gotten any sleep in the past several weeks. In between travelling with their sister, standing guard, and the days spent searching the town for her he must be nearing his breaking point. Given their background it takes a lot to get there but contrary to the personas they try to convey the Zoldyck family is still human and occasionally fallible. And when put under long-term sustained stress they can still make mistakes.
That fact becomes obvious when, even though Illumi is openly watching him, Killua slowly falls asleep, sitting up in his seat. He's still incredibly tense, arms crossed over his chest and eyebrows drawn down but after about an hour Illumi sees his body start to slide slowly backwards as his body relaxes a bit.
Illumi is behind him instantly, careful not to move the seat or touch Killua and instead he lets him fall backwards until his head hits Illumi's chest. Though he seems deep in his sleep one of his eyes opens at the gentle contact. He blinks when he sees Illumi and then closes his eyes again.
The peaceful moment lasts for about a fourth of a second before Killua eyes snap open, and then he's moving over to Illumi's abandoned seat. He doesn't go back to sleep after that, choosing instead to glare either at him or the road outside the window like its wronged him somehow.
When they leave the car their driver is smart enough not to look Illumi in the eyes.
It's early enough in the morning that there aren't any tourist around when the two of them arrive. Killua shoves open the Testing Gate himself, ignoring Zebro's polite "welcome home, Killua-sama" as he cuts through the woods. He looks ragged and angry with actual bags under his eyes that Zoldyck's don't typically get. It isn't until he's stepping through the front door that Illumi sees him finally starts to relax.
"Alluka," he says quietly. He runs across the room to hug her, lifting her off her feet. Illumi notices that the front entrance, which would normally be full of people bowing and offering to make him breakfast, seems to have been quarantined off, and the only other people there apart from the three of them is their mother. Only her head is visible as she watches them from behind the door leading to the dining room.
"Illu, sweetie, what's going on here?" she asks, voice shaking. "That thing has been running loose around the house for days! What are we supposed to do with it?"
"Hi Mom, nothing to worry about," Illumi says. "Alluka was feeling homesick so I helped her out."
"Alluka is that true?" Killua asks, finally putting Alluka down. "Did he make you come home?"
Alluka shakes her head. “I'm sorry, Oniichan,” she says. "I didn't mean to scare you. I asked Illu-nii to help take me home."
“It's okay Alluka. We don't need to stay."
"Actually you do," Illumi says. Killua stares at him from over Alluka's head. "Alluka agreed that it'd be in everyone's best interest to never leave home again."
Killua's expression goes cold, the same defiance in his eyes that Illumi saw when he'd hunted the two of them down with Hisoka. He gives Alluka's shoulder a firm, reassuring squeeze.
"It's okay. It's not your fault," he tells her. He has no real way of knowing how much of it Illumi's fault but the accusation in his stare is unmistakable.
Well, it doesn't really matter how he looks at Illumi. Alluka can't leave - even if Illumi were to burn their house down Alluka would stay and she and the monster that shares her body would burn to death. Even if Killua kills him, even if his father punishes him for it, it doesn't matter, the thing is contained.
And, more importantly, Killua had promised Alluka and himself that he'd stay with her forever.
"I'm sorry," Alluka says, wiping her tears on her sleeve. "I'm sorry Oniichan!"
Illumi turns to leave the two of them alone for now. The sooner they get the tears and the disappoint out of their systems the better they'll be able to adjust to their new normal. For Illumi the estate is small enough that he'll be able to sense them as long as they're within its walls so he can give them some pretense at privacy while they mourn for themselves.
"Oh Illu," Kikyo says, a handkerchief pressed to her visor. "You did something terrible didn't you?"
"Yup," Illumi says walking past her. "Have you had breakfast yet? I thought I'd make pancakes."