I think the box contains a gith knight who saw the "ascension" that lich girl promises. Seeing the soul eating caused him to start a rebellion and the gith patrol is part of the rebellion. Which is why he is at odds with Laezel. Overthrowing lich girl or just a rogue gith army can be useful to Shar. It probably caught her attention because what greater loss is their than having your soul destroyed by being devoured. You don't even make it to the realm of judgement with the wall of souls. Most evil collect souls while very few are cruel enough to destroy one. Funny enough devils and demons mostly recruit and torment too. Even evil gods have little use in destroying a soul. Kill you? Sure. Torment? You better believe it, but destroy is on another level.
It's also why squid people will always be unanimously hated by literally everyone including gods. Unless, of course, they give squids the "literal hell spawn" treatment. "Oh they are good now because reasons ". Pft
