>>12576021Ar Tonelico and Ar Nosurge revolve around song magic being sung each battle to build up their strength and cast increasingly powerful attacks, and while the singers (Reyvatails in Ar Tonelico) are singing, the defenders are other characters who attack enemies as well as defend them from attacks targeting the singer.
All of them do have some romantic development between the MC and one of the Reyvatails (both to build stronger song magic and for specific pairing ends). Ar Nosurge is actually pretty hilarious in that Ion is mechasexual (provided you didn't/couldn't play Ciel Nosurge and marry her).
Reyvatails of Ar Tonelico are some sort of magitech cyborg (physically human, capable of reproducing, but bound by magitech to the towers they reside in in order to use song magic and to interface with certain machinery); the Alpha 3 being fully human-created and tower admins, the Beta series mostly human-created, and the rest hybrid children between Beta Revyatails and humans (and have the shortest lifespan since their human genetics can't handle the strength of song magic).
AT1 and 2 use sprites while AT3 and AN use full CG models.
Randomly; I'm torn between Jaquli and Cocona for AT2's love interest. I like both of them more than AT2's two main Reyvatails.