@Xylo Well, you and the mangaka obviously disagree since she keeps repeating this old story. If it wasn't relevant, then chapter 14 would have been the last time we saw Ookuma's mug, but Coco has insisted on keeping Ookuma's presence relevant to the story. What the eventual outcome may be, we will only know as it happens, but Ookuma certainly does pop up at the most inopportune times for Igarashi.
Just on this holiday trip, for instance, Ookuma's presence has certainly put a damper on Chiyo and Igarashi's relationship. Let's not forget it was solely up to Chiyo whether Ookuma was invited to come and, despite declaring that she didn't want to see him again, she had Igarashi invite Ookuma, anyway. Instead of Chiyo and Ookuma doing the test of courage together, it should have been Chiyo and Igarashi. Instead of Chiyo and Ookuma having a rendezvous in the middle of the night, it should have been Chiyo and Igarashi. Chiyo and Ookuma acting familiar has obviously affected Igarashi, and not in a good way.