How do you buy a Glimmering Drift Shadow?

It only takes an Irisalis transmog as far as the third step, the headgear slot.

Drift Shadows are the free material for rolling and unlocking Irisalis transmogrifications, which change its colours. The shop lists the item as Glimmering Driftshadow, the shop tab is also called the Glimmer Store, and the transmog menu shows it as the yellow material, sometimes named Shimmering Driftshadow. They are all the same item. The purple one is Radiant Dreamshadow, which costs 200 Lumin Crystals in the item shop and is paid for with real money.

You never need real money for a Drift Shadow. Glimmer comes from ordinary play, and daily tasks and events are the quickest sources. The daily activity rewards alone include 30 Glimmer.

Where free rolls stop

Past the headgear slot, the transmog track needs Radiant Dreamshadow. Locking any transmog slot also stops free currency being used on that reroll track, so every roll after that is paid. The transmog menu can untick the free currency toggle by itself, which means a roll can spend paid currency without you meaning it to. Check the toggle before every roll.

Drift Shadows are cheap next to other things the Glimmer tab sells. Capability Fruit costs 1,000 Glimmer there, for example. Glimmer income drops sharply once one-time rewards run out and around level 58 to 60, so it gets scarce in the endgame. Buy Drift Shadows when you are actually going to roll with them, not as a habit.