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Arima was a half-human, an abomination, and a weapon, so something like a birthday was never really celebrated. Of course he had one, but it was meant for official CCG forms and a way to track his age nothing more then that. He did get the odd happy birthday over the years from partners, but never a cake or someone to spend it with that is until Haise.
He had a lot of regrets in his life, but one thing he wouldn’t regret was ripping Kaneki Ken from his life to become his successor, his beacon of change in the world. He was dying, and no ghoul would follow a man known for killing their kind, Eto was the only one crazy enough for that. But, Haise always made him feel guilty on his birthday because while on paper Haise’s was April 3rd, it was really the same as his December 20th. It was Haise’s blissful ignorance, that made Arima sad, because he didn’t realize he was getting older, he couldn’t keep track for himself. But Arima did Haise was 22 and he himself was 32 and they were spending it just like they did every year in a conference room.
“ Do you like it?” Haise asked his eyes wide with anticipation as he watched Arima take a bite of his cake.
“ It’s delicious Haise.” Arima told him his lips upturning in a small smile.
“ I’m glad, I tried a new recipe that I found, but I couldn’t taste it to make sure it actually tastes good.” Haise rambled to him.
“ You did good, but I will admit I like everything you cook.” Arima admitted making Haise beam at him.
“ I would have made you an actual meal but I thought you might like a cake a little better since you don’t eat them often.” Haise told him, as he shifted his weight forward.
“ Are you sure this is not an attempt to sabotage me, so you can finally beat me during sparring.” Arima joked lightly.
“ Of course not!” Haise exclaimed in horror. “ It’s not like I could anyway Arima-san.” Haise muttered a second after.
“ You will beat me someday Haise. I truly believe you will surpass me.” Arima encouraged.
“ Probably not for a billion years”
“ Haise, the CCG would not have left the hope of the future in your hands if they didn’t think you were strong, to teach those who are to surpass me you yourself will hav..”
“ Okay Dad.” Haise interrupted lightly waving him off causing Arima to laugh a little bit.
“ Are you ready to fight?” Haise asked jumping onto the table.
“Haven’t you ever heard it’s not good to fight your father.” Arima scolded as he climbed up as well.
“ You're the one that started this tradition Arima!” Haise yelled.
The fighting went like it usually did, Arima very quickly noticing every flaw in Haise’s stance as well as his movements. While little things have improved like the strength in his defense he was nowhere near fluid enough in his motions to not give away every strategy in his mind.
“ Your not fluid enough, make your stance stronger a strong ghoul could have killed you by now.” Arima yelled to him.
“ Okay.” Haise responded trying to correct it, with small improvement. Arima watched and played with him a little longer as he mentally made a list of all the things that Haise would need to improve. When the list was long enough Arima moved to do what in many ways hurt the most taking Haise down. Taking him down was always the worst, because in the brief moment that Haise is knocked to the ground pen at his face, there is unimaginable fear. That self consciously he remembered everything that Arima did to him, Arima always kept his pen aimed at him scared that he would get his memories back before he was ready. Before, he could put all the pieces of his plan together, so Haise can move forward easily. But, like the last time and the time before that, he would just smile at him and then laugh.
“ I’ll just have to try harder next time Arima-San.” Haise told him as Arima stepped back offering Haise a hand to get up.
“You need to work on your footwork, your not fluid enough so you easily give off a tell of what direction you are going in. Your moving from offense to defense isn’t smooth as well so in even a minimal change you leave yourself open for attack. Also you need to get better at understanding when and when not to use heavy attacks.” Arima advised.
“Okay, thats a lot, but I will work my hardest to improve.” Haise smiled.
“ I just want you to succeed.” Arima gently patted Haise on the back perking him up.
“Oh Arima before we get back to work I have one more thing to give you.” Haise told him him practically skipping to his non quinque briefcase. Haise opened it reaching for the item, trying his best to hide it from Arima’s view, as he walked back to him with his hands behind his back.
“ I got this for you. Happy Birthday Arima-san.” he said handing over a wrapped gift, which Arima almost robotically opened shocked by the gesture.
“A book.” Arima stated obviously.
“It’s Takatsuki Sen, I personally don’t like her works much, but I thought I would give it to you to try, since you seem to like darker books.” Haise clarified.
“ I thought it would be nice for you to have a book you didn’t have to worry about returning.”
“ Thank you Haise.” Arima told him genuinely as he approached his things to collect them, to which Haise followed.
As he and Haise parted ways to go back to work, Arima felt himself saddened by his encounter with Haise. Because as much as he doesn’t regret what he has done, he regrets getting so close to him. It makes it harder on him to know he is going to leave someone behind when he dies, someone he cares about greatly. This was new territory one that he wasn’t expecting when he killed Kaneki Ken. He wasn’t expecting to find love for another human in his life, yet here he was. It hurt watching Haise improve because it was just one step closer to a goodbye, one that will bring Arima both great peace and sadness. He brought Kaneki into his life as Haise to kill him, but never expected to care so much. As much as he tried to rationalize that it would be Kaneki walking out of this, how once he got his memories back he would hate him. But, as much as he tried to seperate them he couldn’t deny that Kaneki Ken was a part of Haise, and that he hoped when Kaneki Ken returned a part of him would hold onto Haise
“ Happy Birthday Kaneki Ken.” Arima whispered to Haise’s retreating back.