Other than the buried accessories (which are never explained) the story is fairly simple.
Komarisa leaves home after growing old enough but can't get out of the terrarium. When Komarisa tries to climb out, Anon removes its accessory and pushing it back in. Komarisa tries to go home but without its accessory, its parents fail to recognize it and chase it into the corner. Komarisa digs into the ground and finds a bunch of discarded yukkuri accessories. In the end, Komarisa slowly starves to death as it watches its parents eat.