Because the arche is a modified version of throne Zwei, one of the first three mobile units to use GN-T and after being upgraded a new one wasn't installed. There is no reference to Arche ever using Zwei's frame, and its always been noted as a successor unit. The reason why it uses the old red type particles is unknown. Several theories include: - Ali likes the old tuning because its poisonous, and part of his sadistic nature. The new Tau Drive beams are no longer toxic, an improvement over the old one (2307-2312 Mission Complete, MG GN-X manual)