I think the ml and his class was involved in a bus accident during their school trip or so...

I think the ml and his class was involved in a bus accident during their school trip or something but only the ml survived. Also, the cause of the incident might caused by the ml (like playing ball in the bus and it hit the driver which caused the lost control) and that's why he's being haunted by "other students" stating why he shouldn't be happy etc..i dont know if this is correct or nah but i think this is just the typical plot that i had read before..but hopefully it would be different from other stories