How do they equip them?

[Forge]

One needs to complete the Bernie Subplot, which involves talking to Bernie a lot of times - although when he does tell you his name, he say's it's Barnie. It also involves you telling Sue your name, so it means that you cannot get the Soul Eater in that difficulty though.

Still for the extension of Soul of Steel, and the second version of it - this progresses the storyline incredibly.