The Forgotten Heir

The protagonist is the eldest son in the family, but his parents always favor his younger brother. After his father dies in an accident and his mother is severely injured, he tries to raise money only to discover that his hard-earned savings have been squandered by his girlfriend and brother. In a moment of desperation, he saves the female lead and, after giving her a blood transfusion, discovers that he has the rare Panda Blood type and is not his parents' biological child at all.