Is it his mother?!
Warning: Spoilers ahead!
Nope, it’s a new characters called Uda Mamoru. If Migi matured in Shinichi’s right hand, the parasite, aptly named ‘Parasite’, matured on the Mamoru’s chest, which uses his mouth when conversing with them. It’s annoying and funny that whenever Mamoru is about to say something, it is being hijacked by Parasite.
It was an accident that primarily led to Mamoru’s predicament as he was attacked by Parasite while on a cliff. Due to the surprise of the attack, they both fall on the sea below and the parasite thinking about its survival, helped him and in turned matured on its chest area. As Shinichi tell his tale, it was clear that Mamoru is a crybaby but wants to help Shinchi’s predicament.
In the middle of the night, Shinichi was awoken by Migi with a important message which involves his body. It explains that his body is now divided in Shinichi’s body and 30% of it is in his blood stream as a consequence of his actions in saving him. It also explains why Shinchi doesn’t need any glasses or why he was able to run very fast. It seems that Shinichi is really bothered by not being a 100% human anymore as it already changed something inside of him that despite still having his brain, his other functions are not the same anymore.
While contemplating on what Migi had told him, Mamoru called him suddenly, informing him that the parasite that he was looking for is in town. Shinichi asked him to run as it kills anything that is not wholly parasite. But, before arriving to where they were supposed to meet, Migi falls asleep leaving shinichi with a transformed hand that can help with their attack.
Mamoru is then cornered on a cliff and Shinichi’s mother arrives to kill them. A fight ensues and Mamoru has suffered an attack to his chest, which led to him falling (again) over a cliff. Is he for comedic relief of this gruesome anime?
Shinichi arrives and his mother was shocked that he survived her attack. She had noted that his parasite is sleeping, as if in hibernation mode, but was surprised that Shinichi was able to evade each of her attacks easily. In one of his attacks to kill, he saw his mother’s burnt hand that made him hesitate — making it known that he was still human with emotions still intact. His mother then attacked him and made him loose his balance.
Before his mother makes the devastating blow, an attack from behind her decapitated her head and the body falls on the sea below. Mamoru is alive! HORRAY!
Now that the threat is over and his father is finally discharged from the hospital, they returned home with hopefully a new lease in life.
This episode clearly depicts closing a chapter of Shinichi’s life where it immitates the changes that had occured and the changes that he is now experiencing in his body.