- “He's a man who walks ahead of me.”
- — Tsukishima Kei, about Yamaguchi.
Tsukishima and Yamaguchi are both first years and members of the Karasuno High School volleyball team. The two first met when they were younger, Tsukishima standing up to those who were bullying Yamaguchi. They later met when joining a volleyball team during junior high, and their friendship developed from there.
Yamaguchi refers to Tsukishima as "Tsukki," hence their ship name. However, it's known that Yamaguchi used to call Tsukishima "Kei-kun" when they were children. The two have a very close bond and are in the same class as well. It is noted that Yamaguchi is also close with Tsukishima's older brother, Akiteru, as they call each other by their first name. They are also seen eating lunch together on multiple occasions.
Especially in the beginning of the series, Yamaguchi usually just follows Tsukishima. Over the course of the manga and anime, Yamaguchi works himself up to Tsukishima's side however, which Tsukishima acknowledges and even sees Yamaguchi as further ahead of him due to his hard work and dedication.
Yamaguchi's and Tsukishima's first and so far only fallout was during their Tokyo training camp. Even before that, Yamaguchi noticed that Tsukishima wasn't taking training and volleyball seriously. This lack of commitment is at its peak during the training camp, which doesn't go unnoticed by Yamaguchi. Thanks to Hinata, Yamaguchi builds up enough confidence to finally express his anger and him trying to convince Tsukishima to take the club seriously. They end up having an argument, Tsukishima being of the opinion that it doesn't matter if you try hard, you will lose anyway at some point. Yamaguchi snaps and yells at him that pride is enough of a motive for working hard. Tsukishima is impressed by Yamaguchi's growth, smiling genuinely as well. Even though Yamaguchi's words left a lasting and big impression on him, only after he talks to Bokuto and Kuroo in the third gym, Tsukishima starts to work harder and more passionately for volleyball.
Yamaguchi has been more confident to yell at Tsukishima whenever he thinks he isn't good enough, after the Shiratorizawa match for example, or just to be generally more confident to express his opinions around Tsukishima.
In Chapter 298 they successfully pull off a "Serve and Block", which was a key moment in their relationship. The chapter focuses on their relationship, past together, and shows how much they've grown. They both high five after their victorious combo, Tsukishima genuinely smiling while doing so. Their friendship remained steady since then.
TsukkiYama is the fifth most popular ship within the fandom and the most written ship for both Tsukishima and Yamaguchi. It is regarded as a very healthy ship, the connection of them being close and childhood friends, as well as their current character development building of of each other's support and guiding giving them no problematic aspect. Adding to the health aspect, their general aesthetic in the fandom is very endearing, supportive, loving, "soft" and also "fluffy"
TsukkiYama is often portrayed as the moon and the stars. Tsukishima's name meaning "Moon Island" and being also canonically shown as or at least with the moon. Yamaguchi doesn't mean stars and hasn't been shown to represent them, but a lot of fans love this concept. This is due to him always being around Tsukishima, like the stars around the moon, and his freckles as well, which are considered to "look like stars" by fans and Tsukishima in fanfictions.
In most fan pieces, Yamaguchi is often the first one to realize, or develop, feelings for Tsukishima. There are many fanfictions and artworks of Yamaguchi's love actually being unrequited, however, in most cases Tsukishima secretely returns the feelings and they work it out. A popular trope in fanfiction/artworks for TsukkiYama is also Angst. A lot of it deals with Yamaguchi's insecurities from the canonical content, especially about his freckles.
Tsukishima is usually portrayed more as the dominant part of the relationship, due to his more cold, collected and blunt personality, as well as him being taller than Yamaguchi. Adding to this, Yamaguchi posesses the more "feminine" traits such as a sensitive, shy and anxious nature, while also being a bubbly, open and generally more joyful person than Tsukishima.
Even though this is the case, there are many occurances of Yamaguchi being dominant in fan art, writing and especially doujinshis. This could be due to Yamaguchi being shown to lead Tsukishima the right way of taking things seriously, often by yelling at him. He's also seen slightly "worshipping" him, especially in the beginning of the series, and thus expressing dominant behaviors. Many fans also enjoy the concept of Tsukishima's quiet nature being a trait of shyness and him getting flustered in intimate situations.
However, TsukkiYama is a widely balanced ship with many fans indeed having a preference for dominance, but not minding each concept. The ship itself isn't regarded as very sexual in a matter of fact and consists of mostly "fluff" and relies on other softer concepts for fan pieces such as art and writing.
- “Shut up, Yamaguchi”
- — Tsukishima
- “Sorry, Tsukki! (gomen, tsukki!)”
- — Yamaguchi
- “Motivation? What do you need more than pride?!”
- — Yamaguchi to Tsukishima
- “I never thought I'd see the day...Just when did you become such a cool guy?... You're really cool.”
- — Tsukishima to Yamaguchi (response to previous quote)
- “I never thought for a single second that I would be able to win by myself”
- — Tsukishima to Kuroo, Yamaguchi standing behind him
- “I can think of a lot words but uncool definitely isn't one of them!”
- — Yamaguchi to Tsukishima as he was about to say "I'm so uncool"
- “Hurry up, Yamaguchi. I'm gonna lock you in.”
- — Tsukishima
- “Are you stupid?”
- — Yamaguchi to Tsukishima
- When Yamaguchi's voice actor was asked what type of person Yamaguchi is, they replied with "they love Tsukki very much"
- Tsukishima usually gets annoyed at people who call him "Tsukki" and tells them to stop, but Tsukishima has never minded Yamaguchi calling him that
- Yamaguchi is also seen getting annoyed at people who call Tsukishima "Tsukki" other than him
- Yamaguchi says "Tsukki" 55 times in the span of the first three seasons
- The fandom has declared the 12th of November to be TsukkiYama Day, probably a combination of their jersey numbers.
- There was a supposed interview with the author of Haikyuu!! going around where they confirmed Tsukishima and Yamaguchi have been dating since junior high, however, that interview was proven to be fake.
- The two met when they were younger after Tsukishima stood up for Yamaguchi when he was being bullied. When they met later at a junior volleyball club, the latter thanks Tsukishima for rescuing him, however, Tsukishima did not remember this incident.
- In the earlier days it was known as TsukiYama, but there have been many misunderstandings and confusions due to the character "Tsukiyama" from the popular series Tokyo Ghoul, so fans switched to TsukkiYama which is now the more widely used term for this ship
- They are usually paired together in official art and merchandise, Tsukishima side eyeing Yamaguchi in multiple pieces
- Tsukishima is often seen with his headphones on, however, he doesn't wear them when walking home with Yamaguchi
- In the Haikyuu!! parody manga "Let's?! Haikyuu!!" there's a panel of Yamaguchi taping the entire clubroom walls with posters of Tsukishima, probably a parody on Yamaguchi's admiration for Tsukishima
- Also in "Let's?! Haikyuu!!", there's a scene where the members try to wake up Yamaguchi, but he doesn't react at all. However, as soon as Daichi says "Tsukishima made pancakes for Yamaguchi", Yamaguchi is seen to immediately jump up with passion