So... I heard you want to make a wish... what's that? you want to relive meeting your best friend for the first time except this time not to be protected but to protect? Sure... easy as reversing the flow of entropy. But first... Take this! It's dangerous Ahead!
(okay... after building this for myself, i found that there are several design flaws... i will fix these)
Opened shell model to come...
Print out one connector and large bump, then print out two of each shard, the arm band and the small bumps.
Remove support material from bumps.
Sand/Dremel the shards and connector to fit.
Use ABS Juice/Acetone to glue the shards together first, add the connector over the top of the glued shards, again glue with ABS Juice and paint.
Remove support material from small bumps and paint the top half.
Place small bumps in the small sockets and glue, again with ABS Juice.
Heat the two arm bands and bend to fit snugly around forearm (make sure not to bend the joint between them.)
To wear, slot the two sides together, insert through the doughnut, slot the large bulb into the connector and twist to lock.
For lazy and unwearable version, download "Homura Shield" and scale down to buildable size