Boothill was roaming before he fell into a portal making him go to another universe where he was born as Peruere, the curse he got was a side effect from the portal and he lived his life while trying to figure out how to get back, he found out that in Penacony it has only been a few days since he disappeared and soon came when he killed Crucabena, he became a harbinger but still hid his identity from even the Tsaritsa. He later found how to go back but figured it would be alarming if he suddenly disappeared from Teyvat with no traces so now he's living a double life (like Gru lmao) one day he was sitting in Snezhaya before the Astral Express landed there and all the harbingers saw..

Childe: Guys look..! Dottore: Interesting.. Capitano: ... Columbina: too busy singing Pantalone: I wonder if I can buy it.. Pierro: Hm... watching it closely Pulcinella: just existing Sandrone: Talking with her robot