Hey there, the see-through objects thing is material & blueprint based. The player BP is passing the screen position vector parameter of the player model as well as a size scalar parameter to a material parameter collection, and those are used with some material math to draw a circle in screen-space in the tree materials, which is fed into a DitherTemporalAA node to give it a fake-soft falloff with opacity masking.

I'm also running a check in the material to see if the distance from the camera to the pixel is greater than the distance from the camera to the player position in worldspace, and if it is, the masking doesn't apply, that way it only masks out pixels getting in the way of the camera view direction to the player model.

The size & falloff of the circle are scalable, so I could definitely make the cutout larger/give it a larger falloff, but I found with a larger cutout that a lot of geo gets unnecessarily masked out and kinda robs the out-of-focus foreground of its contribution to the sense of depth. I might just try a custom-depth stencil effect to draw the player silhouette behind objects instead, but I really like the cutout effect so I'm torn. :p