It is a secret technique of Tenshinryu.
Tessa (手鎖/鉄鎖) is generally called Fundojyutsu(分銅術).
Tessa is the basis of Kusarigama(鎖鎌).
When traveling, Shirindan(士林団) hung Tessa around her neck and carried it.
They used a hook on one side of Tessa and attached it to the sword Tsukagashira(柄頭).
Prepare in advance and use it as a fighter during battle.
It was particularly effective in the dark.
This is especially useful when using a Kodachi(小太刀).
You defend your enemy’s attack with a hidden chain, remove it, and add counterattacks at the same time.