This is an idea of a story I could make revolving crossover between 4 games with it's story loosely based on Persona Q: Shadows of the Labyrinth. Here are the games (and characters) of my choice...

Xenoblade Chronicles

Shulk

Fiora

Reyn

Sharla

Dunban

Melia

Riki

Fire Emblem Fates

Corrin (F)

Sakura

Takumi

Camilla

Elise

Hinoka

Ryoma

Leo

Xander

Persona 4

Yu

Yosuke

Chie

Yukiko

Kanji

Rise

Teddie

Naoto

Tales of Vesperia

Yuri

Repede

Estelle

Karol

Rita

Raven

Judith

With the characters set, what about the setting? Well, I was thinking that the 4 parties will find themselves inside a giant floating castle (IN SOACE!) where they have to traverse 7 dungeons, each with a unique theme, but you can tell me your ideas of a setting. However, I already have the dungeons set and I am only revealing 6 of the dungeons because I want to make the 7th one a surprise. If you want to know what types of dungeons they are, then here is a list...

Dungeon Name - Theme

Land of Sleep - Wonderland

Temple of Desire - Greek Mythology

Dunes of Avarice - Arabian Nights

Palace of Hate - Japanese Folklore

Excess Station - Science Fiction

Infernal Battlefield - World War

? - ?

Can you guess the overall theme of these dungeons and what the 7th dungeon's theme is? Let me know if you like this concept and if you want me to make it. I'd also like to see your own ideas with this concept.