I'm with other people in thinking that it wasn't actually cheating, but a difference of expectations and a lack of communication on Mao's part.
Just because Mao loves other women doesn't mean she didn't genuinely love Hikaru. Some people do be like that. Their feelings are not necessarily shallow, but they have a lot to share and don't feel like limiting themselves to a single person.
Saying "I love you" doesn't mean "I love you exclusively" in my book.
It reminds me of Tsuzuki in Brides of Iberis, who was in an open relationship with two men, and would have had no problem adding a woman. But Kashiwai was more of a monogamous person, so they broke things amicably in the end.
The only thing we can reproach to Mao here is that she didn't make things clear from the start.
last edited at Mar 4, 2023 2:21AM