Parts of the tune to the 2019 anime's first opening (especially the guitar riffs) are similar to the tune of the opening of the 1969 anime.
In the 2019 anime, Hyakkimaru is deafblind for the majority of his life. Though he does have a Disability Superpower with his sixth sense, the ways that Hyakkimaru interacts with the world are more realistic than in the manga (where he communicates through telepathy).
Upon learning he's deafblind, Dororo tries to communicate with Hyakkimaru by using a version of the Tadoma Method. Dororo puts Haykkimaru's (fake) hand to his cheek and throat, trying to get Hyakkimaru to feel the mouth movements and vocal vibrations as he speaks. This is a method that can also be used to teach oral communication, and was one of the communication methods that Helen Keller was taught as a child (along with tactile signing and Braille).
Many deafblind people are capable of living independently and traveling by themselves, as Hyakkimaru does. James Holman traveled the world and wrote books about his experiences.
Written communication is possible from a deafblind person. Most modern deafblind people use Braille or TAPAC to communicate, but there are other options as well. Japanese, being a logo graphic system that historically was based on pictures, could also (theoretically) be used as a tactile writing system.
after getting his hearing back, Hyakkimaru is overwhelmed by all of the sounds able to pick up on things Dororo can't. A similar thing can happen when a deaf person gets a cochlear implant, at times due to where they're placed, the person can hear things like their blood rushing around their skull which can get overwhelming.
Not only that but most people have had a long practice in unconsciously classifying sounds according to degrees of importance and ignoring what we consider to be white background noise.
There is also the off chance hs father's dealing with the demons left him with better senses than usual.
still blind in episode 5, Hyakkimaru misses the first time grabbing a sword offered to him.
come episode 7, he starts using his hearing to help communicate with Dororo. Most of this is just stopping him talking, or a hand movement to get him to stay put. But it's progress.
In episode 9, Hyakkimaru speaks briefly, twice. In the first instance, he only says "Dororo..." to a traveling man while carrying the unconscious kid on his shoulders. The man, reasonably creeped out, ignores him and moves on. In the second instance, Hyakkimaru meets a nun and says, in broken Japanese, "Dororo...body, hot". This all makes sense when juxtaposed against the manga and helps maintain his realistic character development. Hyakkimaru spent most of his life being unable to speak and has the language skills of a toddler.
to add to this there's a slight stretch when he says Dororo, it's either a pause between "doh" and rest of the name or a stretching out of the first syllable. But it's been a consistent stammer since ep 8
In episode 2 Hyakkimaru cuts down a demon mid-gloat. While this may seem like a smart move to catch the demon off guard, it wasn't. Since Hyakkimaru is still deaf all he knew is that the demon had stopped moving(like an idiot) and he wasn't going to let that chance go.
Spending the whole episode with Jukai, we get a good idea of what he was like as a parent, and his emotions in dealing with that fact that Hyakkimaru's innerthoughts are very one-track and seemingly in humane as he's unable to look at the bigger picture of what getting his body parts back would mean. Jukai even goes as far to destroy a wooden leg Hyakkimaru was asking for in hopes to prevent him from either hurting others or ending up alone and no better off than the demons. It's here Hyakkimaru starts to confirm his humanity, actually going off topic to talk about Dororo. And his final interaction is to ask Jukai his name, something he has never been shown to care about when meeting other people (they normally just tell him their name becuase that's normal human interactions). Ashamed of his past, Jukai refuses to tell him so Hyakkimaru instead simply says "I know who you are, you're mama". Showing just how much Dororo has opened up Hyakkimaru to being human. Since the child talks much more about their own mama than their father, and she is the first time we see a parent willing to work hard to give their child anything.
Actually that's been coming up a lot more in the show: The moth thing, evil splinter, Dororo's mama, Hyakkimaru's mother. All parents who will do whatever they can for their children.
On a sidenote, episode 17 concludes Jukai's arc in a poignant manner. The episode is bookended by a demon that ignores Jukai at the start (killing an older man and some scavengers instead), but later bites him in the ankle after Hyakkimaru fatally wounds it. This in turn causes Jukai to cry with happiness instead of sorrow. The symbolism here is that Jukai felt 'dead' throughout his life for his past actions, but Hyakkimaru gave him a new perspective on what it means to live again, redeeming him in the process.
Some people speculate the reason Hyakimaru lashes out at the samurai for killing Mio and the other children is not only out of pure rage, but as a way to try and get her back. His whole life, he kills demons in order to get his limbs, senses and other parts of his body back, perhaps he thought somehow the same could be done for Mio. Gods know what he will do if he ever succeeds in killing the last samurai who killed her and discover that Mio still haven't "returned" to him after that.
Why does Hyakkimaru have hair, and how is it so long? Hair follicles are based in skin, right? Which he didn't recover until his mid-teens. But we see in the flashback he had hair that got longer as he grew up, and there's no indication of it ever being a wig.
Maybe the demons just saw no value in having it? And considering that Hyakkimaru got a sixth sense and survived against dehydration and didn't turn into a mummy as a baby hours after birth, it's safe to say that a lot of magic was involved keeping him alive to honor the deal. Attaching his hair to his scalp directly is not that much of a parlor trick for demonic forces after all the other things mentioned above.
Nui assumes this is due to the headless Goddess she prays to agreeing to take a hit for Hyakkimaru. It got in the way of the demon taking Hyakkimaru's head. Which might be the talked of demon that missed out on the deal.
After Nui failed attempt to kill herself in order to tone for her sins for not saving her first born son, Kagemitsu order his mens to save her life from dying and get a medical treatment. Does Kagemitsu really care and love her in secret or hes planning to used her in future events if their second son gets killed by Hyakkimaru?