|Appears In:||Yu-Gi-Oh! Underground|
Masato "MasaWan" Yamagami, known in the "Underground" as Jester is one of the main characters of Yu-Gi-Oh! Underground. He is the vice-leader of the Stars Gang and is the best friend of Yukito Ousama.
Masato has blonde hair stylized in a rough fashion, with the top of his hair slightly resembling dog ears, earning him the nickname "MasaWan" (wan being the Japanese sound a dog makes). He also has green eyes. Masato dresses in a semi-formal manner, wearing a blue vest over a white, long-sleeve shirt with black pants and shoes. At school, he wears the standard uniform for Hoshio Duel Academy 2nd Year Students.
Masato is a very excitable person, only needing a small amount of "spark" to get him excited. While often lighthearted and easygoing, he, like Yukito, is prone to undertaking a rather dark personality shift, especially when it comes to members of the Stars Gang. Beyond this, Masato has a rather playful personality, much to the often irritation of his fellow Stars Gang members, but is rather efficient in their activities. This aspect of him is one of the primary factors that led to him being picked by Yukito to be the vice-leader of the Stars Gang.
Previously however, as noted by Yukito, Masato was known to be very pessimistic and much of a "downer". He seemingly changed thanks to his involvement in the Duel War.
Prior to the start of the series, Masato had grown up with Yukito alongside the latter's sister, Yumiko. A few years after Yumiko had gone missing, Masato and Yukito began attending the same middle school, which was around the start of the first Underground Duel War. After an incident that greatly affected not only the pair but many of the people around them, Masato followed Yukito in the latter's quest to form the Stars Gang and stop the conflict around them.
Masato plays a Machinic Deck, based around machine-type monsters, who focus around swarm tactics and sustaining his field using his Machinic General boss monsters. His main aces are Machinic General, Grande Riverero and Machinic General Dragon, that later of which can be Xyz Summoned using another Machinic General Xyz Monster.