The young cousin of the Protagonist and Ryotaro's only daughter. Nanako is a very innocent character, but is usually left at home due to her father's work.

Nanako is capable of taking care of herself and watches TV most of the time. She treats the Protagonist as an older brother and tries to do whatever she can to spend time with the family members.

Nanako mostly talks about the afterlife and asks where good and bad people go. The Protagonist helps Nanako come to terms with her father's busy professional life, realizing that he also missed her mother as much as she did.

In the Hierophant social link, it is revealed that Nanako suffers from an illness that causes severe stomach pain that is not explained. She is the Social Link for the Justice Arcana.

When Nanako is kidnapped and placed into the Midnight Channel, it creates a dungeon based on her thoughts. The dungeon which is formed is her interpretation of heaven mixed with innocent thoughts such as rainbows, flowers, meadows, beanstalks and gates. This fantasized heaven was created in her heart for her deceased mother, whom she misses dearly. She is innocently in denial over her loneliness, seeing as she has her "Big Bro", the protagonist, with her now.

The investigation party does not fight Nanako's Shadow, as Kuma explains that Nanako is too young to have an ego, therefore there is no Shadow to suppress.

During the investigation of Namatame, Nanako passes away and the party blames him for her death; the protagonist is then forced to choose between exacting revenge on Namatame or sparing him. If Namatame is killed, Nanako's death is set and the worst ending will occur. If the protagonist chooses not to take revenge and save his life, Nanako is resurrected by unknown means, although Kuma's involvement is critical in the event.