When I ask how to cure it, the answer I got was it cannot be cured by magic or medicine. It seems that the only way to cure it is through time.
But the burns and scratches were healed and my physical fitness has recovered, so I just feel lethargic.
When I check my stats, everything except defense dropped by 30%.
It seems until Blutopfer’s curse is cured completely, they will stay debuffed. This is the price which I paid for meddling in troublesome things.