I bought this juice carton but I've never seen this type of opening in my life. I'm stumped.
Edit: omg I didn't even notice the "lift" sign, thanks everyone! I did it!
Exactly, lift what’s left in the picture and pull towards you. It will push a hole through the carton with the right part which you can push down to support the plastic a bit.
Note these cartons cannot be closed again. EDIT: they can at least partly, see below
This is giving me flashbacks. These used to be very common here in Germany for ice tea. But they sucked so much, we usually lifted up the edges and cut them off.
Is it from Japan? They love weird packaging. Anyway the box looks simple enough, just stab it with an awl punch. A screwdriver would probably work fine too, or probably just a sharp knife.