The length of Yasuo's sword is about that of a tachi or even an ōdachi. However, he wears it cutting edge up like the shorter katana.
Yasuo [jasɯ̟ᵝo] is a Japanese masculine given name, rendered as 康夫 (peaceful man) in the Japanese localization.
From Old Japanese*yasu-(si) "cheap, easy > peaceful" & *wo "man, boy"
Yasuo is not his birth name, but was given to him when he joined the sword school in an effort to steady his wild nature.
Since his brother is named 米 Yone < *yəna-i "[hulled] rice", Yasuo's birth name might be likewise mundane (e.g. Serizawa Kamo's given name means "duck").
Way of the Wanderer's doubled critical strike chance references Samurai gameplay portrayals in video games.
Yasuo and Karma each speak a different, unrelated Ancient Ionian language, given the lack of sound correspondences & cognates (Yasuo's dialect sounds like broken Japanese, parts of it referencing Kiai)
He references and resembles Miyamoto Musashi and/or Haoumaru from Samurai Shodown via his iconic ponytail design shared with these individuals, where in Musashi's case, it is in reference to the common visual design he is depicted with in fictional media.
Haoumaru himself is based on Miyamoto Musashi as well.
Another note of Yasuo is how his Steel Tempest in the Chinese servers is written/dubbed as 斬鋼閃 (Zhǎngāngshǎn, lit. Slashing Steel Flash), which when read in Japanese with the same characters (Zankousen) is exactly the same name as one of Haoumaru's attacks.
Yasuo's taunt in most of his skins (save for Nightbringer [S|L]'s demon form) involves him in-taking fluids from his bamboo flask, then spitting the fluids on his blade to "bless it". This is a habit shared by Haoumaru in his home series' battle intros.
He references Gray Fox, Samuel Rodrigues or Raiden, all from the Metal Gear series. The last was further referenced in Yasuo's recall animation pose that is similar to Raiden's when he battled Vamp's robots in Metal Gear Solid 4: Guns of the Patriots, where he holsters his blade by the pommel underneath his foot.
Compared to his other skins' attack animations (barring Nightbringer Yasuo [S|L]), this skin has different attack animations, along with only having three animations compared to the other skins' four.
When performing his joke, taunt or dance emotes, his helmet reveals his actual face, thus featuring none of the sound altercations. This is unique to him among the PROJECT skins.
His sword blade turns olive-yellow while Last Breath's bonus armor penetration is active, as opposed to a subtle aura covering his sword.
In this skin, he drinks from a fuel-container which may contain a substance suitable for cyborgs.
Yasuo is an Ionian swordsman accused of treason for allegedly murdering an Elder. He is being hunted down across the island continent under the evidence that the killer employed a wind technique, one that only Yasuo has mastered in the present day.
He crossed paths with Taliyah while on the run, teaching the Shuriman stone mage how to control her powers. When they parted ways, she gifted him a long thread from her handspun wool tunic (the same one he uses to tie his hair up).
Yasuo suspects Riven of being the Elder's killer, as evidenced in interaction quotes with her.