The West got Gundam vs. Gundam, but we missed the chaotic arcade perfection of Rengou vs. Z.A.F.T. This is a fast-paced 2v2 arena fighter. The Japanese ROM features a massive roster from the Cosmic Era, and unlike the sluggish Western mech games, this one plays at 60fps even on original hardware.
The second game came west, but the third—featuring a "nameless" penal military unit—stayed in Japan.
The West missed the entire Z saga. This is the second half of the Z2 story, featuring everything from Gurren Lagann to Code Geass. The Japanese ROM is preferred over potential fan translations because the attack animations are so iconic you don’t need to read the dialogue to enjoy watching a 10,000-ton robot punch a god.
The final Tag Force game on PSP. While Tag Force 5 came West, 6 features cards from the ZeXal era and a full story mode involving the anime characters. Because the rules of Yu-Gi-Oh are universal, you can play this Japanese ROM perfectly using a card database app on your phone.