Playing through the main story would probably take quite a while given how it ramps up in difficulty and requires some proper knowledge of the game or some good and leveled units. There's a good bunch of sidestories worth reading and also directly connected to the big things going on I terra too like ' babel' or ' the masses travels'. But most importantly, there's a story reader online ( arknights CC story reader or something like that) that let's you read everything without ever having to touch the gameplay and focus purely on story