Jhin is the first champion to feature a takedown animation on his Classic skin, via Beauty in Death. It should be noted however that the passive effect is not solely for cosmetic purposes.
Despite being the only one seen in-game, the rose is just one of the many things he sees when killing someone.
The violin for Jhin's theme (followed by a chorus) can be heard while the player is channeling Curtain Call.
The people in Spectator Mode can also hear it, though allies and enemies cannot.
Occasionally when playing as Jhin, at the start of the game (between your team spawning at the fountain and then minions doing so at nexus) you can hear a version of the map's theme that fits the style of Jhin's own.
He will always hum and laugh to it.
It reverts to the regular music at about 45 seconds.
Jhin has some degree of innate magic, as he is able to put magic into his bullets. The gun itself, Whisper, is already magical due to being hextech.
It has been confirmed by a Rioter that his bullets shapes his victims flesh into his choosing or make it move as well as other effects.
Examples would be the four champions (Sona, Garen, Vi, and Zed) chosen to be in his teasers.
Blake 'Squad5' Smith was the Quality Assurance Analyst on Jhin and implemented the camera zoom, facing lock and execute damage to his ultimate. It was his work on Jhin that convinced upper management to allow him design his first champion.
Jhin shows traits consistent with obsessive-compulsive disorder focused on the number four.
His login theme is built around 4-note motifs / written with a 4/4 time signature (each bar is separated into 4 distinct beats)
His name and title themselves have four letters and four syllables respectively.
A fourth wall breaker is that on common computer keyboards (QWERTY, AZERTY, etc.) the keys that spell his name make the number 4 diagonally.
IIII is the archaic and uncommon alternative writing, using tally marks, for the Roman four IV, which uses subtractive notation.
The tally marks engraved on Whisper might be referencing this notation.
When he 'performs' in any given nation he makes four people 'beautiful and perfect'.
"Happiness is a thermally active temporal blaster."
In the Italian localization his selection quote "Cadranno come, d'Autunno, dagli alberi, le foglie.", They'll fall, like Autumn's leaves from trees) references the poem Soldati ('Soldiers') written by Italian Writer and Poet Giuseppe Ungaretti.
"They're puppets. I pull their strings, and then they dance." resembles
"Pull the strings. Watch them dance."
"Behind every mask... is another mask." might be referencing Marty Rubin ("Behind every mask there is a face, and behind that a story."), Kakashi Hatake from Naruto ("Behind this mask... is another mask!") or even Luigi Pirandello.