I've noticed an interesting thing - the ED contains an indication of how close each girl currently is to Ichika
Episode 1:
Only Houki is there yet, who is not running particularly close to Ichika.
Episode 2:
Cecil has joined, and has relegated Houki to the back seat.
Cecil isn't running too close to Ichika either, though.
Episode 3:
Just the same as episode 2.
Cecil is running first after Ichika, and Hoiki is running second.
Episode 4:
Rin joined in as the third girl.
Rin takes the spot right after Ichika, and other than Cecil and Hoki before, she's running very close to Ichika.
Behind Rin, Houki overtook Cecil who is now running last.
Episode 5:
No change to episode 4.
Rin is first, running close, followed by Houki as second and Cecil as third.
Episode 6:
Charlotte joined in.
She manages to get the first place right away, running close.
Houki and Cecil maintain their second and third place, respectively.
Rin seems to have totally fallen from grace, from first in the two episodes before to a meager last place, running as fourth.
