Responses
This isn't parallel world, this is going back in time. Which means the ban from that time no longer exists
I think this theory also acceptable, but in the same time it's mean world revolves around him. And that thought is kinda 'meh'(￣∇￣")
I feel bad for Ban from second before last parallel world. I know how frustrating for Issei to spend his time two months that will ended with ban's death. But how about Ban? He'd been told he would die the next two months, but then he witnessed his lover suicide before his eyes because he wants to change the future. Don't you think it's will make Ban suffer even more? But then, as he (issei) says, he is indeed a selfish person. He just thinking about himsel, and doesn't give a fuck about parallel world that he left behind.