I think this counts towards the impending doom tag.

That's a portable mirror.

More likely, it's "Digging Your Own Grave".

Is this an accurate translation? I'm just a beginner, but it looks more like "It's a little too big, I think" (talking about Katori's clothing size, with respect to Ooi). It doesn't entirely make sense why wearing someone else's clothes would make somebody think they've put on weight.

Arcana55 said:

Is this an accurate translation? I'm just a beginner, but it looks more like "It's a little too big, I think" (talking about Katori's clothing size, with respect to Ooi). It doesn't entirely make sense why wearing someone else's clothes would make somebody think they've put on weight.

Your guess was mostly correct even though the reading was flawed. The kanji「太」does look like「大」but means "fat/thick".