Tadashi had seen Ainosuke eat them when they were young. He knows they're fluffy and sweet, that they’re chemicals mixed with more chemicals, but that they tasted good and had a strange texture. It didn’t matter that he wanted to try them, because Ainosuke never offered one and Tadashi never asked for anything, knowing he was a servant before being a friend. But marshmallows always resembled clouds to him. They look so soft and nice, and he wants to try them.
Tadashi buys marshmallows for the first time (and Oka is a good boyfriend without knowing)