+10
I haven't seen Battle Royale.
However, I watched Sundays and Cybele for the 25th Hall of Fame fairly recently. Here's the review I wrote for it there (it didn't make my ballot though):
This was an interesting watch and I'm glad it was nominated. When it comes to the complex dynamic between Pierre and Cybèle, I figure I'll give my interpretation on the significance and implications of their relationship as there has already been a lot of discussion on this. As others have noted, it's mainly Cybèle who turns the father and daughter relationship between them sexual. Initially, she jokingly suggests marrying Pierre when she gets older, but keeps escalating by making a handful of sexual advances with him throughout the film (which likely occurred due to her young age and her inability to comprehend why her behavior wasn't okay and could backfire). Pierre, on the other hand, doesn't make these advances towards her, nor does he say he's in love with her.
In spite of this, however, I don't think this gets Pierre off the hook. Pierre handled the situation between them quite poorly since he did nothing to prevent or stop Cybèle's behavior as her sexual advances escalated. He instead lead her on and went along with her behavior, especially during the uncomfortably tense Christmas scene at the end where he had an, at best, passive reaction throughout it. Given this, I think it's logical to wonder if he would've escalated (e.g., making sexual advances himself) had the film kept going on. Regardless of his intentions though, while I understand why the two of them wanted to remain together, I think their relationship was unhealthy due to the naivety Cybèle displayed with her sexual advances and Pierre's refusal to put a stop to that behavior. Also, without spoiling anything, I thought the implication at the end gave me a lot more to ponder over in regards to Pierre. While this film doesn't give you the answers on what Pierre's intentions were (Was he in love/not in love with Cybèle?/Did he have malicious intentions?/etc.), it gives you a lot to ponder over and there's a handful of ways one could view their relationship.
Overall, I really enjoyed this film. Its refusal to spoon-feed its intentions to the audience and its willingness to leave them up to interpretation is its greatest strength. This makes the film ambiguously menacing and I can see myself rewatching it down the road.