Like how Alvin was announced, this week’s Shounen Jump has some information regarding the 4th character to join up game’s roster of characters. The 4th character is called Leia Roland, a girl who seems to specialize in healing artes, making her the would-be primary healer of choice in the game.
Described as a girl with a cheerful personality, Leia is a childhood friend of Jude (that male main character) and has a weakness of some sorts for betting on sports and martial arts tournaments. Since Jude is a martial artist, this could probably mean something!
It’s worth noting that most Tales games have support up to 7-8 different characters to form a party (Tales of Symphonia had 9!), so there’s still quite a ways to go until we know them all!