Tales of Vesperia takes place in Terca Lumireis, The Citizens of Terca Lumireis rely on Blastia. Blastia is an ancient civilization's technology with a wide array of capabilities, that range from giving water, powering ships, or creating shields around major cities and towns which provides them with protection from monsters.
Things go wrong when a Aque Blastia Core is taken from a major cities lower district which causes flooding. Yuri Lowell the main protagonist takes it upon himself to catch the theif though in doing so he is arrested by the capital guard. Upon escaping from prison Yuri meets the princess who happens to be looking for his best friend Flynn. After discussing what to do next the princess Estelle decides to join Yuri and his dog repede on their quest to catch the blastia theif in hopes of maybe meeting flynn aong the way.
As they travel the world of Terca Lumireis they will meet and befriend a variety of people who will share a lot of their goals and ambitions. Such as Karol a young boy who joins the group to maybe catch up to his fast moving guild and Rita a Blastia research who is very interested in Estelles healing abilities.
The groups goals eventually go much further than taking back a stolen Blastia Core. The way their operates as a whole becomes a concern and its up Yuri and his team to set things straight.