i never used a microwave before and i dont own one lol
since i usually heat my food using a rice cooker lol

so what its looks like with the food inside when that happened ?

If it's just a little metal in the box (probably just some foil for a side or something), then there shouldn't be any issue. Maybe a couple of brown spots from the sparks.

If it's from HokaHokaTei (or any bentou store) then it comes hot - so there could be metal. Ones from the convenience store are intended to be heated up in the microwave from the get-go.

i see lol
thx for the explanation~