Ito Junji no Neko Nikki

Ito Junji no Neko Nikki (猫日記よん&むー Neko Nikki Yon to Mū) also known as Cat Diary: Yon and Muu is a manga by famous horror manga author Junji Ito and his daily life with his fiancée's cats.

J-kun is not a cat person. He says that dogs are more trustworthy. But he loses the fight when his fiancee A-ko insists they're adopting her parent's cat Yon, and adds Norwegian rescue Mu to the mix. Then he sees A-ko and her mother cuddling Yon, a funny-looking cat with a skull print on his back. A flip switches, and cue J-kun spending a life trying to win over the cats.

Drawn in his usual style used for his previous works like Gyo and Uzumaki, this manga is actually comedy, but with similar visual effects of his earlier works for comedy value.

Tropes used in Ito Junji no Neko Nikki include:

Adult Fear: Rather, cat owner fears when you take in a fur-baby:
- Despite being reassured that neutering is a normal process, J-kun frets as Mu is taken to have his nuts removed. He fears what if Mu dies on the operating table. Fortunately, Mu is fine, just a little disoriented post-anesthesia.
- There's a chapter where Yon escapes outside the house and goes missing. A plumber has to help dismantle part of a warehouse where Yon has hidden. After that, J-kun installs magnetic strips along all the balcony doors and windows. The measures don't stop Yon from trying to pull a Houdini move, though J-kun and A-ko develop fast reflexes.
Art Shift: Some of the chapters in the trade paperback are interspersed with pictures of the real Yon and Mu.
Author Avatar: Mr. J is Junji Ito himself. His future wife is A-ko.
Bittersweet Ending: Most of the collected manga is super cute, and hilarious as J-kun finds himself trained in the way of being a cat owner. The epilogue, reveals, however that Yon eventually died of heart failure, as he was old for a cat. J-kun and A-ko write separate pieces thanking Yon for being in their lives. Junji Ito did follow-up videos with Crunchyroll to talk about them further, as well as other cats he adopted.
Cats Are Mean: Subverted, or played straight, depending on your point of view. Mu is a pretty friendly boy that will cuddle with anyone; J-kun admits he can't get mad at Mu for biting him during a petting session. Yon at first is aloof, but he comes to offer comfort when a deadline and sleep-deprivation cause J-kun to hallucinate.
Cat Scare: A realistic sort; while sleep-deprived and needing to meet a manga deadline, J-kun starts hallucinating monsters around the apartment. He's relieved on seeing that it's only Yon chilling.
Cloudcuckoolander: Mr. J and A-ko chan have their moments of this. Just ask A-ko about the fine art of flicking a feather toy.
Cuteness Proximity: With a healthy dose of Nightmare Face. No kiddin'.
Does This Remind You of Anything?: Despite polar opposite art-styles, the humor is quite similar to Hyperbole and a Half, in part because they're based in the personal stories of the artist.
Four Is Death: Yon's name means "four," and J-kun at first is convinced that Yon is a demonic kitty given the name, the skullmark on his back, and his general attitude. Apart from a desire to escape outside and to steal other people's shares of fish, though, Yon is a pretty normal cat. Sadly, Yon also dies at the end of the manga, owing to heart failure and old age.
He Also Did: Junji Ito is known mostly for his horror stories, like Gyo and Uzumaki.
Journal Comic
Lighter and Softer: Compared to the rest of his works.
Mark of the Beast: Yon's markings on his back look like a human skull. This troubled Mr. J in the manga before he grew fond of him.
Nightmare Face: A-ko, J's wife: no irises, and ALWAYS smiling. Once in a while, J makes one too.
Playing Against Type: This series compared to the rest of his work.
Ridiculously Cute Critter: The manga and real Muu. Not a surprise since he's a Norwegian cat.
Slice of Life