Safety pin

Typically a metal cotter pin like device for keeping a land mine or hand grenade from going off, however in this case it is
used as a synonym for a companion who keeps you calm or from getting upset or "exploding with anger or lashing out'.

"Please stay with me you can be my safety pin.."
(used in Korean movie 'its ok not to be ok)

where military service is required by all and understand how these war devices work