In a Anime World With a Weird System?

Ever since Lin Zhi was sent to a mega-sized anime world, his weird System would occasionally give weird him missions that would send him into the future, the past, or even parallel worlds! [Mission] [Difficulty: A-] [Setting: High School DxD - Great War Era] [Background: You are a nameless participant of the Great War, a war centuries ago, between the three Biblical Factions: the Devils, the Angels, and the Fallen Angels.] [Objective: Participate in the war and survive for the duration of 7 days. During this process, you are not allowed to communicate in any way or form unless forced to, such as incantations for spells. You are, however, allowed basic gestures such as pointing, nodding, and the like. Do not try to find a loophole or else you will be punished as per severity.] [Reward: ???] "So I'm going to the past and whatever I do will affect the present? Does this mean I can even get missions for One Punch Man and even My Hero Academia?"