-( Story related, cannot be missed )-
Chapter 3: After returning to the secret base from Towa Tower, you'll end up getting in a confrontation with Haiji temporarily before the Monokuma start to pour into the secret base. You have several adults to defend with Shirokuma helping out in actual combat by stunning the bears (though not actually killing them, so make sure you unload a few BREAK bullets into them with this opening). You can also use Genocide Jack to take them down faster (depending on if you've spent any spare coins to upgrade her attack stats). Most of them will end up being the basic Monokuma models, but there are some Bomber Monokuma that will appear as well.
NOTE: At least one person died on my game and I still got this trophy, so I'm not sure if there's a perk to keeping them all alive or if you just need to save at least one. Any confirmation on this would greatly help not only me but future viewers of this solution.