How to clean pen ink off the plastic AirPods case?

Hello,

From the above article, using a cloth with isopropyl alcohol will likely be the best option. Different types of plastics have different properties. If the plastic absorbed the ink, and the ink dried before being cleaned off, it's possible you will never be able to remove the stain without damaging the case itself.

How to clean your AirPods, AirPods Pro, AirPods Max, and EarPods - Apple Support

"Clean the charging case with a soft, dry, lint-free cloth. If necessary, you can slightly dampen the cloth with isopropyl alcohol. Allow the charging case to dry. Make sure not to get any liquid in the charging ports. Here are a few more guidelines:

• Remove any debris from the Lightning connector with a clean, dry, soft-bristled brush.
• Don't use abrasive materials to clean the charging case.
• To avoid damaging the metal contacts, don't put anything in the charging ports."

I hope this helps.

If the ink cannot be cleaned off (and I’d expect not), get an AirPods case or a skin.

There are many options for cases and stick-on skins from many vendors, too.

Read and follow “Clean the case of your AirPods or AirPods Pro” in the article linked above.