From the Start, I Had a Tower, and Signed In for Divine Weapons

Lin Qi wakes up to find that he has transmigrated to a post-apocalyptic future, trapped from the start in a thousand-meter tower. The futuristic weapons one by one set his heart racing, but then he learns that human civilization has been destroyed, with only five survivors left, and that they must face endless waves of beasts. He panics. Luckily, the [Daily Sign-In Superweapon] System awakens! [Day One sign-in reward: Gravity Cannon!] Teammate: “Holy crap, you're incredible, boss!” [Day Two sign-in reward: Mutant Cannon!] Teammate: “Boss, do you have room for one more lapdog?” [Day Ten sign-in reward: Causality-Erasing Dagger!] Teammate: “???” [Day N sign-in reward: Conceptual God, Pangu Axe!]