I prefer the backpack mostly, but we can go for the shield.
In my opinion though, seeing how toribash works, if the shield was on the back of the tori sometimes it's just gonna pierce thru his back which isn't too practical you know. A backpack wouldn't do the same since it's a solid object stranded to the back of the tori.

I mean it's still a 3d object, so there will be ghosting no matter how we plan it. But yeah, I think the final vote is backpack. Time to start linking specific backpacks for reference!

Sry about the invade, but what should joint will you guys use? if you put it in chest for example, when you move it the backpack will go into the pecs, you know?
You guys needs to think about it

I made a backpack some days ago in the joint:

I gave up cuz of the second pic

I was actually thinking about the shoulders rather than the pecs but since that happens I guess I can rig it some other way or maybe think of another item...

I was thinking more of a smaller backpack like Melioda's from Nanatsu no Taizai thing, but without the sword.

I'll get some concept art for the bag

Rigging it to the breast body part will work well

Here's the concept art! I made it bulky to show some of the detail a lil more. Ofc, we can mold it to whatever shape we want

How about a belt?

A belt? What do you mean?