Left Hand (左手 aka Countenanced Carbuncle and D's Left Hand) is the symbiotic partner of the vampire hunter D.
He appears on D's left hand as a face on a cancerous looking lump. He is a lot more outgoing than D, and is a polar opposite of the hunter when it comes to expressing his emotions. They share an affinity toward how they would handle most situations as far as combat is concerned and work in tandem as though they are of one mind. He is a bit more cautious than D is and prudent, more likely to take the road of least resistance, whereas D is not as careful or willing to play it safe. He tries his best to watch out for both their well beings.
He is a constant jokester in most situations, though he can be very serious when the situation calls for it. He is often many times colder than D about caring for and helping those in need while other times he is warmer than D about it. It seems this is mostly dependent on his mood at the time. In battle he has a will of steel that is a match or very close to D's. He has not failed to be there for his partner in time of need despite their disagreements from time to time, they have a strong friendship, it seems. Left Hand knows D probably more than anyone he has come across.