The structure of the ship
The structure of the ship, which has dark-skinned people living on lower decks and light-skinned people living on the upper decks, is a metaphor for systemic oppression and racism. Much like the United States through the end of Jim Crow (and many argue such oppression still goes on in the U.S. today), the ship is structurally racist.
Climate change
The situation on the ship - one in which human beings are forced onto a life raft in order to survive - is a metaphor for the situations humans will be forced into should climate change continue to decline due to humanity's inaction.
Aster
Aster is a metaphor for the lived experiences of people of color who deal with racism: she is shy, kept in the dark, unable to speak her mind, and pressured by society to be something which she is not. Aster is a victim of structural racism.
Acquaintances
"I don’t have time to nurse an acquaintance, especially not one as old as ours" is a simile which compares the acquaintance's age to the person's willingness to nurse them.
Glass
"She’s glass. I’m glass. We’re all glass, busted up, unrecognizable from our original selves. We walk around in fragments. It’s a circus act. This is a metaphor which compares the way people on the lower decks feel about themselves with glass, which is easily breakable. Because they are victims of systemic racism, the people on the lower decks were easily broken and intimidated by their oppressors. They are, in other words, easily breakable, and just like glass.
