List of characters who know Subaru Okiya's identity

there are actually up until now 7 people who knows that Subaru Okiya is actually Shuichi Akai in disguise.

Canon

Conan Edogawa/Shinichi Kudo

Conan knew who Subaru was before they even first met, and also trusted him and lent him his house's keys despite Haibara's protest.

Hiroshi Agasa

Agasa is the one who made the Voice-Changing Choker for Shuichi.

Yukiko Kudo

Yukiko is the one who taught Shuichi how to disguise himself as Subaru.

Yusaku Kudo

Yusaku seemed to be informed by his son about Subaru's identity. He even assumed the Subaru persona for one night to lead suspicious away from Akai.

James Black

James was the only member of the FBI aware of Akai's fake death plan as he noticed that Shuichi's fingers were coated by glue. It seemed he secretly kept contact with Shuichi disguised as Subaru.

Jodie Starling

Jodie was able to figure out the plan that Akai used to fake his death, and she managed to figure out Subaru's identity after been told by Camel that one of Akai's catchphrases is " The division of fault is 50/50", the same line Subaru used with Jodie during the Beika Department Store Case after he knocked her down preventing her from chasing after Scar Akai.

Andre Camel

Camel witnessed Shuichi's disguise technique as Subaru Okiya as well as the Voice-Changing choker to modifiate his voice. After that he would give Akai a hand with guarding Haibara from the Kudo house.

Suspicious

there are 4 people who became suspicious about Subaru's identity.

Rei Furuya

During the scarlet showdown,Rei was able to discover the trick that Akai used to fake his death as well as Subaru's real identity and the voice-changing choker used to change a voice. But, Conan was able to deceive Rei creating a scenario where both Shuichi and Subaru, who was Yusaku in disguise, existed as different persons, which made Rei lose his suspicions. However, in Volume 90, Rei's suspicions had been aroused once again as he noticed Subaru is left-handed and remembered Yusaku disguised as Subaru is right-handed as he removed his cold mask with his right hand. At the end of the case , Rei seemed to be more suspicious about Subaru's identity as he told the latter that he can't wait to pull out his high collar, but told him he won't do it until he obtains real proof.

Vermouth

Despite all of Bourbon's plans through out his arc, at the conclusion he seems to have convinced Vermouth that Shuichi Akai is truly dead. However, in Volume 90 she meets Okiya Subaru in person for the first time, while she is disguised as Azusa Enomoto. She seems curious and asks Rei who he is, which is when Rei notices that Subaru wrote left-handed. It is unclear how much Vermouth heard about Rei's comments to Subaru, but later she catches Rei staring at him. At the end of the case she gets distracted by Ran and it goes no further.

Ai Haibara/Shiho Miyano

At first, Haibara suspected Subaru to be a member of the Black Organisation as she was able to sense the organisation's smell from him. However, she changed her attitude towards Subaru after the latter reassured her during Detectives' Nocturne when Conan was kidnapped telling her "Don't make that kind of face, i will not let them run away", which caused her to remember something similiar to what Akai told her about her sister; " Don't make that kind of face , i will protect her at cost of my life". At that moment , Haibara begins to suspect that Subaru is Akai, she also have noticed that Subaru always wears high Collars despite sometimes the weather is hot. She even attempted to pull out his collar, suspecting that Subaru is hiding something on it.

Masumi Sera

Sera met Subaru during Yusaku Kudo's Cold Case and found him very suspicious. She have noticed somehow that Subaru is left handed as he was brushing his teeth with his left hand, which may have caused to remember her brother since Akai is left handed as well, however, her degree of suspicions is still unknown.

Kaitou Kid/Kaito Kuroba

When Kaitou Kid (also known as Phantom Thief Kid) Kaito Kid took a picture of Subaru to have a collection of people he could disguise as, he noticed that Subaru had a machine on his neck. That would be enough for Kaito Kid to guess that Subaru is hiding something, but he is not aware of Subaru's real identity.

Possible

Hidemi Hondou

Hidemi helped Akai faking his death. However it is unknown if she is aware of his new identity as Subaru Okiya, but she does have his phone number, which she used to inform him of Rum.