Now, it's been something akin to a running gag- Atsushi's thoughts and feelings on Akutagawa.
He'd sit around, hidden under the kotatsu that he really should put away since the cold season is almost to an end, during his off days, clasping a warm bowl of chazuke that reminds Atsushi of life around him; he'd sit around and ponder and think and wonder like what old men do whenever their young ones leave the nest. (well- Kyouka was starting to leave the nest since she was going back to school to meet other people her age, so perhaps that could count.)
He'd sigh, eat a small portion of his chazuke while nursing a cup of green tea, leftover from what he poured into his bowl. Chazuke was always Atsushi's favorite food, but eating it in such a disheartening state- he was actually starting to become worried that his routine of thinking whilst eating was destroying his favorite meal for him. (He dearly hopes not.)
Like any other important thing in Atsushi's life, Akutagawa was a mystery that he is intimidated by. He wants to solve it, oh Atsushi really does, but- he does not have the capacity nor the means to solve it. He does not have the courage to confront and ask Akutagawa about it (rather, he actually has a little self-preservation left contrary to public opinion and he'd rather would not want to be sliced and diced once more. He can heal, thank god, because of the beast but the pain of being gutted like a fish wasn't a nice and relaxing thought. He still felt the pain you know!)
"Ugh." Atsushi frowns as he sets aside his empty bowl of chazuke and clasps his cup of tea. He blows on it, and then takes a sip from it. Green tea was really rather nice in contemplating things, especially if the subject in itself is also a bit bitter with a hint of sweetness underneath. He sighs in happiness as he feels the warmth of the green tea spread throughout his body. (Oh my- perhaps he really is becoming an old person.). He puts the cup down and continue his business.
What on earth was Akutagawa to him? Atsushi did not know and did not dare to answer just yet. The mafioso was one who would always without fail continue to always confuse the hell out of him. Atsushi was sure that he was an enemy but to what extent?
They often worked together, often talked to each other, often fought (but it wasn't as common nowadays as it was back then), Akutagawa sometimes visited Atsushi to give him something like a bag of sweets and Atsushi would sometimes also invite him over for some tea. (Kyouka was wary at first, but seeing the bag of sweets Akutagawa always had made her brighten up and loosen up, and Kyouka taking Gin like a fish to water was also helping immensely), and when their jobs took to the late hour (which was always) they sometimes went home together, walking underneath the moonlight with their surroundings a calm and relaxing quiet.
Strangely enough, Atsushi felt this strange feeling blooming in his chest recently. If he could describe it, perhaps it would be a stinging? A good stinging that brought him pleasure instead of pain. His cheeks often reddened as he thought of his rival, which Kyouka often commented on not knowing what her brother was talking about. ("oh! are you seeing anyone in your life atsushi? the reddening of your cheeks tells me so!" she'd often teased which lead to atsushi burying his face in his hands in embarrassment.)
Perhaps-
No! It's impossible!
But-
Hmm. A contemplative thought-
Maybe?
Perhaps he was feeling something other than platonic feelings for his co-worker/rival. Perhaps- and it was wack for Atsushi to even consider this, but he is left no choice.
Perhaps he held romantic affections for the other? Somewhere along the way- that platonic affection and that toleration for the other somehow twisted and morphed into something- something that was bring Atsushi the greatest of worries but the greatest of pleasures.
Kyouka would laugh to be honest, then would proceed to 'subtly' (read: not subtly) tease him in front of Akutagawa. (He loved her like a brother would to a sister but she was often- she was often like that. It is all in good fun though, so Atsushi would just smile at her.)
"Aah!" Atsushi shouted out in frustration, his face was now red as a cherry and hidden by his fingers. This would perhaps prove a problem to the stable working relationship he and Akutagawa have; in all honesty, he would rather die than to compromise that.
He frowned, slumping over the kotatsu, frowning at his cup of green tea long finished. Life was unfair-!
(in a distance, a mafioso would sneeze and shiver against his black coat and white scarf. he would rub his nose and then bundle up even more, slightly tugging on the ends of his scarf and trying his best to not shiver more against the cold. he was overly dressed but for some reason he could still feel the kiss of the freezing day.
"gotta get this mission done." akutagawa says, talking to himself. his nose was as red as rudolph the reindeer and he was sure he might catch a cold as he just sneezed, not thinking that perhaps someone was talking about him. "wouldn't want to catch a cold.")