To get the sword. I believe you need size and strength. AKA muscle. Someone please correct me if I'm wrong. As for how much you need to put into those stats to get the sword. I'm not sure, but I believe it's Beyond 100.
To open the locked chests, you need chest keys. Which some enemies randomly drop them, or you can talk to someone that can randomly appear at the start of the ruins on each floor. Which will have Chest keys.
They usually have 5 and I think they're 25 Demi dollars per key.