[Katsuki perks up a little bit when Hijikata asks that question, seemingly a little excited that Hijikata recognized the necklace.]

Oh, uh... yeah. He gave it to me for my birthday.

[Katsuki sits up a bit, so he can hold the pendant in his hand.]

He told me to keep it safe, so I'm keepin' it on my person as much as I can. Which I guess is a good thing, 'cuz it'll come in handy with the power out.

[Even though he's completely forgotten that it illuminates flowers until this very second. He's been so busy with everything else... he'll have to give it a try after they're done bathing. Katsuki doesn't particularly need the light anymore, but it could be comforting in a time like this.]