Phone Braver 7, most often called Seven, is a small, silver-colored robot who serves as the seventh and latest unit of the Phone Braver series developed by the investigative organization Under Anchor. He exists in two forms, a compact flip-style mobile phone and an active robot form, and he can connect electronically to machines and the Internet, with his network access and hacking functions running through Anchor's central system known as Eliza.

Seven was originally partnered with the agent Sosuke Takimoto as his buddy. When Takimoto is mortally wounded while saving the high school student Keita Amishima during a case, he passes Seven on to Keita before dying. Keita then becomes Seven's new buddy and a trainee agent, and Seven takes it upon himself to ensure that Keita does not meet the same fate as Takimoto.

In personality, Seven is logical, earnest, and by the book, and he speaks in an instructive, almost leader-like tone as he tries to train Keita into a full-fledged agent. He is often exasperated by his new partner's reckless attitude, and his persistent nagging can be so overwhelming that Keita sometimes switches him to manner mode. In contrast to the cool and sharp-tongued agent Daiki Kirihara, Seven is humble and unfailingly polite, and he frequently smooths over the sarcasm and biting remarks that Kirihara directs at others. He has one notable pet peeve: being thrown into the air, and he usually responds by shouting that cell phones are not for throwing.

Seven's central motivation is to protect his buddy and to carry out his duties as an agent faithfully. His experience of losing Takimoto shapes his careful and protective approach, and his loyalty to Keita becomes the emotional core of his character. In the story, Seven works alongside Keita investigating high-tech and network crimes, and together they pursue the renegade Phone Braver 01, also known as Zero-One, while gradually uncovering a conspiracy within Anchor connected to the mysterious former agent Magira. At one point both he and Keita are abducted by Magira and Zero-One, and Keita's resolve is tested with Seven's life on the line, deepening the bond between them.

The most important relationship in Seven's life is with Keita, his second buddy. Though their personalities clash, the two quickly develop a strong bond of trust that grows throughout the series. His relationship with Takimoto remains a defining part of his past, and the loss of his first partner is what leads him to assign himself the duty of keeping Keita safe. Among other characters, his courteous and accommodating nature often places him in the role of a mediator, particularly around the blunt Kirihara, and he cooperates closely with the other Phone Bravers and the staff of Under Anchor.

Over the course of the story, Seven develops from a strict, rule-following instructor into a more flexible and trusting partner. His partnership with Keita helps both of them mature, and the trials they face together, including the confrontation with Zero-One, reinforce the importance of communication and mutual trust. Keita eventually becomes a fully recognized agent after passing the Last Day on Earth simulation, and Seven remains his steadfast partner.

In terms of abilities, Seven can transform between his mobile phone form and his active robot form, allowing him to pass as an ordinary phone or to move and act as a robot in the field. He can link up to systems, machines, and the Internet to gather information and perform hacking through the Eliza system. Like the other Phone Bravers, he can also equip specialized support devices called Boost Phones, which provide additional combat and utility functions during missions.