Chapter Text
The afternoon sun cast long shadows across the Demon Slayer Corps headquarters. A light breeze rustled the wisteria blossoms, adding a touch of serenity to the usually tense atmosphere. Tanjiro, beaming with pride after a successful mission, bumped into Giyuu Tomioka near the training grounds.
"Sorry Aniki. Oh, I mean... Giyuu-san!" Tanjiro's face exploded with crimson. The words had slipped out, a familial term. It echoed a little too loudly in the near silence, attracting the attention of Shinobu, Mitsuri, and even the stoic Muichiro, who raised an eyebrow.
Giyuu’s usually impassive face was now a shade of pink only seen in Mitsuri's favorite mochi. He coughed, straightened his haori, and mumbled, "Kamado... focus."
Tanjiro, mortified beyond belief, bowed deeply. "Forgive my disrespect, Tomioka-san! I must…sharpen my sword!" He practically teleported away, leaving a trail of awkward silence and suppressed giggles in his wake.
Time Skip
Two weeks later, Tanjiro found himself on the receiving end of Giyuu's "Older Brother" Lecture. He was perched on the edge of a tatami mat, trying not to fidget, while Giyuu paced back and forth.
"Headbutting the Wind Hashira? Tanjiro?" Giyuu sighed dramatically. "The Muzan encounter? Absolutely reckless. And what was that stunt with the Rui situation? I’m grounding you from missions for a full week! And Don’t even try to tell Sofu Urokodaki, he agrees with me!”
"You’re Grounding me?!" Tanjiro sputtered. "Tomioka-san, you can't ground me! You don't have the authority! Plus all that stuff happened months ago!"
Giyuu stopped pacing and looked down at him. "As your Aniki, I believe I do." He turned and offered a stuffed bunny with a pink bow to Nezuko, who cooed happily from her box. "Here you go, Imōto. Anything for my sweet new little sister. Are you sure you are not tired?"
Tanjiro's jaw dropped. This was a whole new level of weird. "Older brother? Where did you even get that idea?"
Giyuu, internally reveling in the chance to finally be the older sibling for once, replied with a surprisingly mischievous glint in his eyes, "It slipped out, remember? Besides, I am older than you. I'm just looking out for my Otōto, who has a terrible habit of nearly getting himself and his little sister killed."
"But...I'm the oldest! I'm supposed to be the one looking after everyone!" Tanjiro protested. He was accustomed to being the responsible one, the protector of his family. This role reversal was deeply unsettling.
Giyuu merely shrugged and ruffled Tanjiro's hair playfully. "Relax, Otōto. Let me handle the big things for a change. Besides," he added with a smirk, "someone needs to make sure you don't pull any more of those 'headbutt first, ask questions later' stunts. Now, come on get nezuko, there are rooms ready for you and her at the water estate, and Sofu is going to be arriving in two days to scold you." and walk away.
Tanjiro groaned getting up to follow him. Being an older sibling was stressful enough. But he was about to experience being a younger sibling, especially to Giyuu Tomioka. This "Aniki" situation was going to be a long and embarrassing one, and he knew that Giyuu would use this to his advantage every change he got.