Contrary to popular belief, Tsuzuki thinks of things besides candy. He thinks of pain, his own and those of the people he loves. People he's killed. He thinks of love, of Hisoka, and of guilt about loving. He never wants to cause Hisoka pain.
He thinks of everything he can't say, because somebody might be hurt. He tries to not even think of even those things, when Hisoka is near. It's hard, but he tries to forget.
Tsuzuki thinks of sweets because it's safe. But honestly, he realizes there's something else as well.
There's alcohol.
Sometimes, it's sweet like candy.