Arachnus is a humanoid Yo-kai with pale peach skin, eyes with light green sclera and yellow irises, red Kabuki-styled face markings, black hair with yellow streaks, and appendages that simulate spider legs and a ponytail at the back of his head. He wears a red kimono, a purple kataginu with spider web designs being held by yellow ropes, a dark blue hakama, and white socks and zori sandals.
Arachnus is the general of the Bony Spirits army, in contrast to his rival Toadal Dude, he is more serious and ground-to-earth personality. Despite this, Arachnus is very passionate over sweets (to the point of declaring war after a disagreement on whether custard donuts are better than cream donuts or not) and has no tolerance for spicy foods.
Arachnus and Toadal Dude start out as enemy generals who start out a war against each of their respective factions, after a series of events in Yo-kai Watch 2 unfold, they call a truce and eventually become allies.
In the first movie, Arachnus is one of the many Yo-kai that Nathaniel has befriended, he comes to his aid when facing off against Dame Dedtime.
Yo-kai Watch 2: Bony Spirits
To befriend Arachnus, the player must first complete the game's main story and unlock the Rank S Yo-kai Watch, after that, receive the version-exclusive quest: "The Bony General" from Arachnus himself at Flatpot Plains. Collect a Bun of Oneness, which are rarely dropped by Chymera at the Infinite Inferno or Kyryn at the Divine Paradise and give it to him, which will make him attack the player due to the unexpected spiciness of the Bun of Oneness. After he battles you, he will be automatically befriended, completing the quest.
Yo-kai Watch Blasters
In his mission in Chapter 11, Arachnus can be rarely befriended after the mission is cleared.
Yo-kai Watch 3
Arachnus can be befriended through the quest The Persuasion of General Arachnus, unlocked after completing the quest The Search for General Toadal Dude, through the Detective Agency after Chapter 10.
Alternatively, he can be freed from the Crank-a-kai by using a Legend Coin.
Yo-kai Watch 4
Arachnus can be freed from the Past Crank-a-kai in the post-game.
Arachnus is based on the purse-web spider youkai called tsuchigumo (土蜘蛛, "ground spider"), which is also his Japanese name. They are typically evil masterminds that use illusions and trickery to lure their prey, or inflict them with supernatural diseases. The most famous one disguised as a servant and secretly administered poison to the hero Minamoto no Yorimitsu, until he saw through its illusions and struck it down. "Tsuchigumo" was also a pejorative name for gold miners of the Edo period, who polluted rivers with the mercury used to sift gold, and were thus likened to the earth-dwelling poison-spreaders.
The phrase doton no jutsu in Arachnus's Soultimate is a term describing a group of real-life ninja techniques themed around the earth element, such as curling up and remaining motionless to disguise as a rock.