Just started watching this and thought it would be a fun crossover. I can see it either going Alya or Marinette as the lead, Alya because she likes the abnormal in the series and Marinette because she is the main character. Summary I'll write for Marinette.
Adrien Agreste has long since given up on the supernatural, which all changes when he hears Marinette's introduction stating she believes in aliens, time travelers, and espers. After having conversations with Marinette, she forces him to join her club, along with literary club member Alya, shy and sweet Rose, and ever smiling transfer student Nino. Each of the other club members comes to Adrien telling him they are aliens (Alya), time travelers (Rose), or espers (Nino) who were sent to monitor Marinette, as well as her interactions with Adrien.
Whose Who:
Haruhi - Marinette/ Alya
Kyon - Adrien/Nino
Yuki - Alya/Juleka
Mikuru - Rose/Marinette
Itsuki - Nino/Adrien
Ryouko - Lila