Other than Komari after Refrain, none of the other girls have shown any indication that they are in the loop. As the author had suggested before, Kurugaya’s disposition is a lot more perceptive than the rest. Plus, when the author uses the word strong, that doesn’t necessarily mean physically. Just go back up a few more paragraphs and the author writes Kyousuke being the one with “the strongest willpower and greatest amount of unconditional love for both Riki and Rin”.
It’s due to Kurugaya’s strong will to maintain that closeness she had experienced that causes the loop to continue. However since she was not inherently the host, per say, she has difficulties maintaining the loop and inevitably causes anomalies to occur.
The author doesn’t make any suggestion that Kurugaya knows about the loop, but vaguely aware of it enough to try to make one of her own.
Kengo and Masato also being excluded from the female cast due to their strong bond with both Riki and Rin. It’s fair to say that they would definitely maintain a stronger will power than the other female casts (especially since they didn’t carry any burdens that these girls would have).
I believe it’s because the world was losing its cohesion that Komari was able to retain metaphysical knowledge of the synthetic world. Due to the amount of almost agape state of love Komari had for Rin, she was able to manifest herself for a little bit longer despite the “world” losing its cohesion.