The Riddle Solver who Can't Solve Riddles and The Riddle Solver who Won't Solve Riddles are titles given by 7:24 to the fanmade PVs.
Nazotoki and Nazokake are Hinata Haruhana's biggest hits. On February 19th she uploaded the song Nazotoki, with her as the vocal. A month after, Hinata Haruhana uploaded the 'Vocaloid' version sung by Kagamine Len. A year later, the series was sold on an album called Mechanical Mystery.
Hinata Haruhana has stated that all of her songs are connected to each other in some way. The only confirmed songs to be related are Nazotoki and Nazokake.
Nazotoki and Nazokake are originally stories written by Hinata Haruhana "Umi ha sono nazotoki wo nozomu noka?" (海はその謎解を望むのか？). The ones sung by Rin and Len are the 'Vocaloid' version of the story, in which Len plays Haruka's role while Rin plays Akira's role.
A novel adaptation of the song "Nazokake" written by Hinata Haruhana and illustrated by Yon published from Poplar Pocket in July 2014, is also loosely based on this story; with a similar set of characters, the main difference being the two main characters "Kurono Rin" and "Shirohane Len". A hardcover version of the novel is available later in April 2015.
The series tells about a boy (Shirikawa Haruka/Len) who used to be a child prodigy at piano, and liked a girl (Kuromiya Akira/Rin) for many years. One day the girl's home caught on fire (arson), and the boy saved her, losing his arm in the process.
He continued liking her for many more years, even though he saw her with someone else (Let me Play the Piano?) and in truth the girl liked him too (Snow is Falling?).
Haruka, now assistant to Detective Mikami, and Akira, unknowingly went on the same fancy boat party, by an unknown benefactor. What happened next was a string of murders, such as a man dying from poisoned wine, and people falling into the ocean.
Haruka then discusses the murders with Akira and claims that he did the crimes, while Akira believes he hadn't, and it still remains a mystery...
It starts with a one-armed detective and a girl alone in a room. They were discussing the 'mysteries' that had occurred.
The first mystery is the man who drank the poisoned wine, the detective's 'answer' to that case is "The man knew then that it was his fate to die anyway." meaning the man did that on 'purpose'. The detective kept on asking who the culprit was to the girl, while the girl just listened to him quietly.
The second mystery is the people falling into the ocean, he questioned whether the culprit was in the group as well. "Only another failed plan,that theotherDetective was dragged into." the detective said, while the girl grabbed a knife in her pocket. He asked who the culprit is again, saying everything is right in front of him, he wanted to start solving the mystery with the girl.
The third mystery (which is in the 'long' version of the song), is about a girl. What was in the girl's mind? The one-armed detective narrowed his eyes slightly,
the instant of darkness took the girl's breath away.
Also, in the long version, it was mentioned that the detective knew that the girl had a knife with her. "After everything ended, you, my darling, arrived here, hiding that knife."
which is why he could defend himself easily when the girl attacked him with it.
He said to her that he was the culprit, and also mentioned he didn't want the girl to know. The detective gave time for her to run, if not, he will have to kill her, because everything happened right before her eyes.
The detective only has one arm, some think both are present but that is just a fanmade PV by7:24. In the original PV, lyrics, and story, the detective only has one arm. (See Let me Play the Piano)
This song is in the girl's point of view, she wondered why he kept on hurting himself, thinking he can protect someone.
She then talks about the first mystery, saying there were actually two wine glasses, and even if he didn't die by the poison in the wine, the man would have died by the knife (most likely the girl's knife)
While listening to the detective, she kept on thinking that everything was a lie and doubted that he was the 'detective'. The girl tried taking a shot at the riddle, saying "'He' could only kill them one by one, but still couldn't be the culprit" ('One by one' may refer to the group of people falling down to the ocean)
The girl tried to 'accidentally' kill the detective, and gave her answer to the detective's question: "who is the culprit?" and replies: "The culprit is not you."
The video then shows a building on fire, and the one-armed detective standing on the stair case. She said the detective's arm was used to play the piano, the detective tried to 'save' the girl.
She said that she will solve the riddle, and the detective. Whoever is involved in the mystery, the girl will trap them, "welcome to our world"
Note: This is not the last song in the mini series.
The song starts with Len who said he'll never tell Rin he loves her, he doesn't want her to know, yet he still wants to play the piano for her. As the song goes, it tells that Len saw Rin with a man (Kaito), and he gave her a warm smile. He felt jealous, though he didn't want to be selfish. He chose for Rin to be happy with that person, leaving her alone.
Though he still wished the person walking beside Rin was him.
One of the main reasons why this song is connected is because it has the same illust (where Len's hand was on the piano) in the end of the original video of Nazokake.
The song tells of a girl, who's going to the convenience store. Along the way she sang remembers a boy, the sound of the piano, sadness, full of tears. This may or may not happen after Akira (the girl's) lost her mansion according to the plot.
This song is connected to Let me Play the Piano, because the melody of Let me Play the Piano can be heard from it. Also, by the end of the song, it says 'Please play the piano for me.' (So far there is no Vocaloid version of this, for Hinata Haruhana usually sing the original version first before making a Vocaloid version of the song)
Another reference of this song to the series is the "crescendo" (Let me Play the piano; though it's rather common in music/piano) and also "It is said that you and I are existing across each other in a mirror"
This song has no definite plot, it tells of two people who have different point of views. The main question was "Trick or treat" and Rin and Len replied differently.
Len chose trick, he was bored of the 'game' to identify the 9th culprit. He wanted to be impressed, and challenges you to trap him in the cleverest trick you could make, looking at from all angles, he tells that deduction is a disruption.
Rin chose treat, though she was bored of the chocolate bar she'd eaten three times. She wanted to eat a treat, and asked to give her the finest treat on her tongue, or else you will be on everyone's tongue. Rin said she'd eat you whole, because you look battered, like a cookie.
This is somehow related to Nazotoki/Nazokake because it makes reference to 4 songs from Hinata Haruhan's works as it said:
"Poisoned wine (Nazotoki?) or a silver cake knife (Nazokake?) A soundless piano (Let me Play the Piano?) or snowed muffins (Snow is Falling?) Tell me which would you prefer?"