>>35716909To clarify more, in the presentation, Masuda states that co-op adventuring gameplay is a first for the Pocket Monsters series. If spinoffs were taken into account, then that'd obviously be untrue as games like Gates to Infinity had co-op. Logically, this would imply that he's referring to the mainline series, where the closest to co-op you got was the Battle Frontier in Gen IV. "Pocket Monsters series" is used as a term to describe mainline, in this case.
The translator localized this as "for the first time in a mainline Pokemon RPG", as saying "for the first time in the Pokemon series" would be ambiguous and also cause people to bring up examples of spinoffs with co-op.