The Solar-Trans GX is a Dual weapon for Isa. It is obtained as the treasure of the Star Map in Infinity Blade III. To get it, follow these steps:
1: Purchase the Star Map in the Supplies store.
2: Purchase Siris' Axe of Heaven and Isa's Blade of Heaven (you will need them to access the observatory in which the treasure is located) and go to it.
3: Tap on the object shown in the map and you will obtain the Solar-Trans GX.
This weapon has a square gem slot and also a dual gem slot. Like in all Solar-Trans weapons, it will amplify the power of the gems attached to it.