Digital Pets

Digital Pets are small handheld electronic pets.

Features
The pet appear in pixal form the device screen. Its appearance and personality are dictated by and evolve according to how the owner takes care of them.

Digital pets can connect with each other by touching the two metal pads at the top of the devices off each other. While connected the pets can exchange data, interact and fight.

In the manga the average lifspan of a digital pet is 21 days. The exception to this rule are the rare Black Star pets, which can be recognized by having a black star in their appearance. Black Star pets live much longer than ordinary pets and tend to be more powerful.

Manga
Yugi's pet, U2 interteracted with Jonouchi's pet, Joe. Although Jonouchi's initially bullied U2, they became friends afterwards.

Kujirada had a Black Star pet, Devil Master. Devil Master began to communicate with Kujirada and tried to become the master. It kept him awake at night, demanding food. Wanting better food, it set it's eyes on eating other pets.

When Jonouchi left Joe alone, Kujirada linked it to Devil Master, letting him eat it. Kujirada then grabbed Anzu's pet Peachy and also fed it to Devil Master.

Kujirada tried to let it eat U2, but U2 was able to change into a more powerful form, similar to how Yugi can change into Dark Yugi. This was due to the exchange of data it got from when it interacted with Joe. U2 then beat up Devil Master.

Anime
In the anime, there was a Digital Pet competition, where the winner won a holiday to Australia. Honda took care of a pet for Miho, which he called Super Strawberry.

Yugi and Jonoushi let their pets interact, same as the manga.

Kujirada, who was trying to make his pet strong for the competion, swiped Peachy from Anzu and fed it to Devil Master. Jonouchi then connected Joe, which started fighting Devil Master, but ultimately got eaten. Yugi, Anzu and Miho tried telling Kujirada what he's doing is wrong. Kujirada then tried to take U2 to feed it to Devil Master, but Honda arrived. After spending 3 sleepless nights taking care of Super Strawberry, he connects it with Devil Master. Super Master sweeps Devil Master away.

Haiyama, who had been using Kujirada as his own pet, later attacked Yugi and his friends and tried to turn Honda into his new pet. This caused Dark Yugi to emerge. Dark Yugi connected U2 to Haiyama's pet. The game became a Shadow Game and the pets appeared as real beings. Using data it incorporated from a connection with Jonouchi's pet, U2 upgraded form like Dark Yugi and was able to defeat Haiyama's pet. Haiyama started whipping his pet, telling it to get up. For Haiyama's Penalty Game, he imagined the pet turning on him and eating him.