I WILL TRY MY BEST! I'm not actually too familiar with how these two would interact? It's a lot of fan interpretation but I'm gonna go in my own direction, so hope u like it <3!
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Rui was a patient man, though the same could not be said about the spirit that stuck around him. While Gashadokuro usually only made itself known in Rui's company when he needed its assistance, there was an exception to this policy, and that was when a certain trio came to mind.

"Tsukasa-kun~" he purred, blowing some air into the other's ear from behind, sending the boy almost flying into the atmosphere from how high he jumped, hand covering his ear defensively before relaxing upon seeing Rui's face. "Ufufu... did I scare you?"

"Rui! What are you doing here?" Tsukasa ignored his teasing, though his face reflected a slight tint of red covering his cheeks. "I thought you were busy today..."

"Mm... well, I was supposed to be, but I have a bit of a situation that you may be... familiar with?" He lifted up a fox and a tanuki by their backs, both animals struggling in his grasp (the fox seemed rather irritated, but the tanuki had let out a whine or two of pain).

"Oh!" he gasped, taking the two into his arms as they situated themselves on him. "I didn't realise they wandered off... I'm sorry, Rui!" While his apology seemed genuine, Rui chuckled as he leaned in a bit closer to his face, a hand raising to lower the other's glasses slightly and stare deeper into them, his eyes shining slightly.

"Oh Tsukasa-kun! Who do you take me for? Your little friends were more than happy to indulge the real reason they came to bother Gashadokuro... next time, perhaps it's best to just admit you miss me?" Tsukasa flushed at the accusation, mouth opening to retort but shutting upon realising he had been figured out.

The two familiars snickered at his sides, while Tsukasa pulled gently at their ears in a scolding manner. They were tricksters, but certainly they would've learned how to keep a secret! Still, Tsukasa just pouted, kneeling to let them go as they curled around his feet, and Rui lifted him back to his full height, hands cupping his cheeks.

"Well then, Tsukasa-kun~ If you missed me so dearly, how about we spend the rest of the day together, just you and I? I'm sure our dearest companions can entertain themselves. I've been missing you dearly, after all~" He pressed a gentle kiss to the other's nose, and Tsukasa chuckled, placing his hands on top of Rui's wrists.

"If you insist, let's go do something fun then."