Is Ar no Surge related to Ar Tonelico?
Warning, some spoilers for Ar Nosurge are below:

Ar Nosurge is set in the same universe as Ar Tonelico, but not on the same planet as Ar Tonelico (mostly, two of the main characters do visit Ar Ciel, the planet in Ar Tonelico). It is also a prequel to Ar Tonelico (the plot of Ar Nosurge takes place around 700 to 800 years before Ar Tonelico).

Despite being set on a different 'planet', there is a major story link between the two, as it deals with the origin of the Teru tribe in Ar Tonelico. You also meet a major character from Ar Tonelico in Ar Nosurge.