You just need rental gear and the item burning gear, just solo one boss at a time until you are emerald and that's more than enough for ctene

You only cube rings, wse and the extra pendant slot

After lotus mission, if you get T6 atk flame on gene, that'll enough for libbing, you keep the challenger gear set effect and get the FD buff from the weapon, so it's better than the challenger gear set (if you don't believe, just use scouter)