Of all the Keybearers, Isa gets along best with Aqua.
She is the only one who deigns to speak to him – other than Lea – but unlike with Lea, there's no tension that hangs over the room, suffocating Isa's lungs.
Most days, Aqua talks to Isa of her life. Isa privately enjoys this time more than his time with Lea. Lea never wants to talk. And if he does, then he tries to talk about their childhood; and Isa is in no mood to reminisce. Ever.
Sometimes Aqua asks about Isa's childhood. Isa doesn't reply to these questions.
Other times, Aqua cries, and Isa is reminded of the sister he once had. Aqua would have liked his sister.
Isa tries his best to comfort, but he is a man made of icicles, and his half-formed, half-meant words do nothing to staunch Aqua's sadness.