Cadin is automatically befriended in Welcome to the World of Yo-kai when the player captures bugs. They figure that one of the bugs is glowing not noticing that it is Cadin. Cadin revealed himself after the player meets Whisper and receiving their respective Yo-kai Watch model. He only revealed his true self when Nathan wakes up a Buhu. Impressed with the payer's bug-catching skills, Cadin offers his Yo-kai Medal, allowing the player to fight Buhu.
Cadin can be found on Stage 11 of Uptown Springdale. Furthermore, he can also be found on Stage 46 of Blossom Heights, and on event stage 2 and event stage 8 of Mystery Way and on Stage 17 of Super Mystery Way.
Cadin can also be freed from the Crank-a-kai with either Pink Coin or Cheerful Coin.
Yo-kai Watch 2
Cadin can be found on trees around Uptown Springdale and trees near Owl Light Road in Shoppers Row.
Cadin can be found in the second Quiz Room behind the 40 Gate Globe Gate of Whimsy which he always appears at the bottom middle tree.
"Semimaru" combines semi with maru (丸), a suffix typical of boy names. It might also be a wordplay on Semimaru, famous poet and musician of the Heian period. In Spanish, "Ningarra" is the combination of the words Ninja and Cigarra (Cicada).
Cadin's design is based on a cicada, specifically the Japanese species called minminzemi, after its "min min" cry which is also Cadin's catchphrase. (Said species is also a catchable bug in the game, called Green Cicada in the US port.)
Cicadas are especially known for their courtship calls, which are particularly loud (up to 120 dB, one of the loudest in the animal kingdom) and usually performed at dusk to avoid the attention of predators. They're regarded as one of the symbols of summer, and in past ages, both them and crickets would be kept as pets for people to enjoy their singing. They also give their name to a type of ninja decoy techniques (typically removing one's overcoat and luring the enemy into striking it), called utsusemi no jutsu ("cicada skin technique").
Unlike how Jibanyan, Dismerelda, and Happiere were the first three Yo-Kai Nate meets in the anime, Cadin is the first Yo-kai befriended by the player to fight Buhu.
In the E3 trailer for Yo-kai Watch, Cadin can be seen attacking, still using its Japanese voice. This was changed by the time the demo and final game were released.