The girl on the right is Princess Kaguya, the protagonist of one of Japan's oldest extant folk tales. (It's one of those things where, this old couple adopts a child, she grows up to be The Most Beautiful Woman In The World, then gets revealed to be a princess from the Moon -- it was written back when that kind of story was still original.) In Touhou, her full name is Kaguya Houraisan, and she got banished to Earth 1300 years ago for using a forbidden elixir which makes her literally unkillable.
The smoker is Fujiwara no Mokou (that's "Mokou of Clan Fujiwara" basically), who has just the most BREATHTAKING hate-crush. She stole a dose of the elixir for herself as revenge for Kaguya rejecting Mokou's father's hand in marriage. She nursed a grudge for about 900 years until she found where Kaguya was living on Earth. Now they regularly get into fights and "kill" each other.
I SHIP IT.