This sketchbook entry was clearly preparation for this comic
The immortals are dressed in late 18th century upper-class clothing, and their ears are clearly extra long and droopy. While an elven-like look is one of the reasons for their pointy ears, the reason it is common for immortals to have big noses and ears is because I've been told that people's ears and noses continue to get bigger as they grow older. This logically lead me to conclude that immortals would have big ears and noses, though I've clearly set some limits on how big their sniffers get.
I wanted to give some personality to the sarcastic ass older student beyond being a sarcastic ass, so he got the added depth of being an annoying tourist. Okay, that's a bit unfair. He clearly spent a lot during his trip to France and presumably knows the language, so perhaps he's a welcome variety of tourist. Probably still annoying, but hey, at least he's supporting the local economy.
For this scene, young Susan and Nanase needed sleepy-time clothes (that's the scientific term for such things) . Susan wearing basic pajamas with pants was a no-brainer, but Nanase was a bit trickier. Her wearing something dress-like made sense, but I didn't want to put fifteen year old Nanase in a nightie or anything like that. So I went for the over-sized-yet-fitting shirt look, something that looks comfortable for sleeping while covering her up nicely. I find it a believable choice as something she would elect to wear if sharing a room.
...Wait, which comic did I link to? For reals? Oh. I meant this one