Soft Boiled Eggs
Artist's commentary
Hang in There, Kogasa-san 2546
It's apparently called an eggshell cutter. I'm ashamed to say I didn't know about it.
It takes quite a bit of time for the eggs to become nicely soft boiled, so I got in the bath, snuck in eating some anmitsu, etc. The hot spring eggs were super-tasty, too!