Shoulder Massage Holder-kun

Shoulder Massage Holder-kun (肩揉みホルダー君) is a contraption sold in Japan apparently used to massage the shoulders of its wearer.

Principles
It is famous enough to be advertised in the top-selling weekly manga magazine in Japan and in late-night mail order television. The device looks like a U-shaped plastic device, which was probably around 15 to 20 centimeters long. The U-shaped portion would fit directly over the shoulders when it was used, and came in an economic set of two (in the magazine advertisement).

Academy City Invasion Arc
Aogami Pierce shows Kamijou Touma a magazine article about it mentioning how it looks cool and he might get one as his shoulders had been sore. After Tsuchimikado Motoharu begins arguing with Aogami about whether it would be useful or not, Touma suggested they mention it to Fukiyose Seiri to get another opinion as she has frequent shoulder aches and likes mail order products.