Sekine invites Chiyo to a sleepover at her house, and the other two invite themselves as well. They deepen their bond while Rikka learns more about the quirky cultural activities that take place on Earth.
From context, I can imagine it's something 
that involves a gathering of people...
Ich gehe davon aus,
Por el contexto, imagino
Por el contexto, imagino
Vu leur réaction,
Dal contesto,
Pelo contexto, eu posso imaginar que
é algo que envolve juntar pessoas...
Судя по контексту, это некое действо,
для которого люди собираются вместе…