No worries about cracking the shell even if you get on a crowded train! I found a cute case for boiled eggs and bought it.
An egg-shaped case called "boiled egg holder ghost". You can put one boiled egg with a shell. Since the case contains a silicone cushion, it is possible to protect the boiled egg from impact. It also comes with a strap and salt container that are convenient to carry. The size of the egg that can be stored is "up to M size", but it may not fit due to individual differences.
A boiled egg holder that is easy and safe to carry and looks cute. Since there are many parts, the amount of washing will increase, but why not add it to your lunch box goods? Sales locations are various EC sites. I bought it using Amazon.co.jp and the price was 540 yen.