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 spiderweb designs being held by yellow ropes, a dark blue hakama, and white socks and zori sandals.
In contrast to Toadal Dude, Arachnus is more serious and strict in nature, he has a very articulated form of speech.
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.
Receive the Bony Spirits-only quest: "The Bony General" from Arachnus himself. 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. After he battles you, he will befriend you automatically, completing the quest.
Loafing: "Break time."
Befriended: "Splendid. You shall be my friend."
Traded: "So you need assistance? I'd be happy to lend a hand...or eight."
Receiving food (favorite): "Amazing!"
Receiving food (normal): "It was OK."
Receiving food (disliked): "No more...please..."
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.
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.