I'm told the context is not clear, but if you've seen/played FSN you'll remember that Saber's weapon was initially invisible, and that she loves food. That's what the pun plays on.
Huge (invisible) candy
note: it says ふ菓子, which is お菓子 ("okashi": candy), with the standardized honorific "お" replaced by "ふ", so that the reading becomes "fukashi", invisibility (normally written 不可視)
