This third part reveals that Micheal has been manipulating Yuuka and Tatsuya separately all along; in the previous parts when Michael blackmailed Yuuka over the photo she sent Tasuya, which Micheal found out in the routine checks due their school's draconian policies against dating amongst students so even personal belongings can be inspected.
It now shows Micheal took advantage of Tatsuya's guidance seeking over his stagnant swimming numbers and his personal erectile dysfunction problems to rope Tatsuya into his little game, first showing he knows Tatsuya and Yuuka are secretly dating after finding out about the photo, which makes Tatsuya mad at first but Michael is an expert manipulative person, making Tasuya know getting mad won't solve anything if Michael decides to report, thus Micheal devises a plan to get what he wants (sex) and rope Tatsuya into getting over his erectile dysfunction frustration before Yuuka finds out her boyfriend can't perform by instigating a cuckold fetish on him.
Turns out Micheal wasn't off the mark, Tatsuya was mad their coach was blackmailing him but a sudden feeling of arousal over the prospect of Yuuka getting taken starts to surge, thus everything that has been happening in the previous parts were all known to Tatsuya, and here in the third part Micheal and Tasuya decide to come clean to Yuuka as she sees the door opening with Tatsuya looking at her with Micheal, she at first tries to desperately apologize to Tatsuya but he calms her down, now morphed into a full fledged cuck who has accepted this ordeal as his penis has been harder than ever and his worries have subdued.
Their relationship has become twisted, but Tatsuya reassures he wants to be with the Yuuka who is handled by coach Micheal, Yuuka is finally fully developed into going along with it without feeling guilt, reassuring Tatsuya she loves him when he finally participates along with Micheal in taking her at the same time, even trying to cheer him up after Tatsuya says he can't compare to coach Micheal by saying he is dick and skills are not bad, she loves Tatsuya so if he wants to see her being taken so be it, so please watch Yuuka's ass being taken to the fullest she says; ending with Yuuka and Tasuya now fully "developed" into better swimmers and lovers who can be open with themselves as coach Michael handles them without ever reporting the young couple to the school faculty.