You are ALL wrong! The one that gets the xp is the one doing the kill! Yes, Missile-kun gets the xp, becomes a max level missile in the game, then after he kills the last boss and dies, he gets iskeied into another world as an OPed missile!
Depends on how xp party sharing is set, maybe, just the leader gets it or maybe only the one who pushed the button or maybe all those who got a say in the matter get a fraction of it, etc... XD
By that logic, it self destructed and achieved a mutual death. No exp, unless it transfers over to its isekai adventure.
From my understanding: The one who launches the nuke/triggers the mechanism should get the EXP if it's a autonomous weapon after it receives the button press/order. Like the laser-point missile systems or GPS steered ICBMs. If the weapon needs to be fired & aimed, the one who controls it should get the EXP, like how the AC130 operator does in Call of Duty Modern Warfare. If the weapon deployment is voice controlled then the one who gives the order.
Ah I forgot about that to, pokemon was easy af even without it but with it you end up overlevelled even when you try to actively avoid it... I meant more along the lines of switch training in the earlier 2d games...