Blacksmith Vincenz:
Alright. you can use a Soul Crystal to bestow a special ability onto weapons. There have been some changes to the Soul Crystals, and now you can upgrade them by combining them. That's why we have new Soul Crystals now.
The Soul Crystals from before cannot be used anymore. You can get the new Soul Crystals by defeating boss monsters, so remember that.
If you need more information, check the instructions.