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It's called a "hera." In certain ways of wearing hakama, the obi gets tied in the back (rather than in the front as seen most commonly in aikido). The "hera" then gets tucked in between the obi while the koshiita then goes above the obi knot.
You can see this tucking in the sixth image on this page:
It should not be removed under penalty of the law. It is kind of like those tags you find on a pillow. If you take a chance and remove it, you may find yourself surrounded by 300 armed men and two tanks. In gassho
I haven't removed mine but I don't use it. At a summer camp I saw a spectacular hakama failure when somebody stepped on the back hem of their hakama and ripped the hera (thanks Jun) off which also opened a huge hole just below the koshita.
"A pacifist is not really a pacifist if he is unable to make a choice between violence and non-violence. A true pacifist is able to kill or maim in the blink of an eye, but at the moment of impending destruction of the enemy he chooses non-violence."