I'm kinda surprised that I've never heard any VN players ever refer back to the beginning of EP3, when the kids are all hanging out on the beach together. The Anime (understandably in this case, would be hard to adapt well) removed some of the nuances of that scene, but it really strongly indicates how little about six years prior Battler actually remembers. I couldn't find any clips on YouTube of this scene, so I recorded my own - beware sucky quality and lack of audio, but it's the dialogue that really matters here:
Six Years Ago
When I first began EP3 and got to this scene, I could tell it was a little suspicious and found some of what was said strange, but having gone back and read it again now with knowledge of EP4 and Battler's sin, it strikes a
lot closer to home. I recommend Anime-only viewers check it out, because I think it provides some strong hints as to Battler's sin. I can think of at least 3 or 4 different potential theories in this scene alone.