Dramatic irony
There is a dramatic irony in the novel Someday because only readers know that "A" inhabits the bodies of different characters. For instance, Rhiannon, Ethan and Alexander do not know that "A" has transformed into their bodies on various occasions. Consequently, David Levithan lets readers know aspects that his characters in the novel are not aware of.
Situational irony
The situation irony is prevalent in Rhiannon and Alexander's sexual relationship. Alexander loves Rhiannon wholeheartedly and looks forward to marrying her in future. Ironically, Rhiannon is deeply in love with "A," who has disappeared, but hopes she will return to rekindle their relationship. In addition, Alexander does not know that Rhiannon is a lesbian.
The irony of Poole
Poole, referred to as "X", can switch his body into different forms to impersonate people of his interest. Poole poses as a handsome white guy to lure girls like Rhiannon into his trap, and he later harms them. The primary paradox in the context is that "X" hates fellow people with the ability of body switching like "A." Instead of forming a relationship with “A,” Poole ensures she permanently disappears.