Koichi Hirose
Also known as: Koichi
Koichi Hirose is the audience-perspective character of Diamond Is Unbreakable and the franchise's only depicted Stand User who recurs across two consecutive Parts. A short, unassuming Morioh middle-school student whose Stand Echoes evolves through three Acts (each with distinct abilities), Koichi serves as the team's narrator across Part 4 and is sent by Jotaro to Italy in Vento Aureo's opening chapters to retrieve a DNA sample from Giorno Giovanna.
Story
Diamond Is Unbreakable
Part 4 · 1999Koichi is one of Josuke Higashikata's classmates at Morioh Middle School when Stand-related disturbances begin in spring 1999. His Stand Echoes awakens after Keicho Nijimura strikes him with a Stand Arrow during the Nijimura-house arc, and Koichi joins Josuke's protection collective alongside Okuyasu, Yukako Yamagishi, and Jotaro Kujo.
Across Diamond Is Unbreakable Koichi serves as the audience-perspective character — the manga uses his observations to introduce new Stand users to the reader, and his Echoes evolution across three Acts mirrors the arc's three-stage structural rhythm. His role in the Kira investigation is critical: Koichi's ACT 3 evolution provides the team with gravity-modification combat unmatched by any other Morioh Stand user, and his late-arc combat against Kira in the Kawajiri house is the manga's structural argument that the audience-perspective character can carry direct combat responsibility.
Vento Aureo Opening
Part 5 · 2001Two years after Diamond Is Unbreakable, Jotaro Kujo sends Koichi to Italy with instructions to retrieve a DNA sample from Giorno Giovanna — biologically DIO's son via the Joestar bloodline body. The mission opens Vento Aureo and is Koichi's most-recurring single-arc appearance outside Part 4. His Echoes Stand provides crucial early-arc combat support before the Bucciarati crew takes over the protection-of-Giorno responsibility.
Powers & Abilities
Echoes
StandEchoes is a humanoid Stand whose ability evolves through three discrete Acts across Diamond Is Unbreakable. ACT 1 projects onomatopoeic text (sound-effect words like "BANG" or "DRIP") that produce the corresponding sound when peeled away from a surface. ACT 2 projects sound effects directly into a target's body, producing physical sensations matching the word (a "BURN" tag burns the target, a "CRUMBLE" tag causes brittle tissue collapse). ACT 3 is the most-combative form: a small humanoid Stand that multiplies the gravitational weight of any target it touches, with the multiplication scaling up to compress targets through floors and walls.
The three-act evolution is the franchise's first depicted stage-Stand mechanic — the structural template that Tusk's four-ACT progression in Steel Ball Run and various Stone Ocean Stand-evolutions inherit. Koichi remains the franchise's only depicted Stand User with three discrete Stand-stage personalities — each Act has its own attitude and combat voice, distinct from the others.
Relationships
Allies
Trivia
- Koichi is the franchise's only depicted Stand User to recur across two consecutive Parts as a main character. Most Stand users appear in one Part only; Koichi's Diamond Is Unbreakable presence extends into Vento Aureo's opening chapters via the DNA-retrieval mission Jotaro assigns him.
- His Stand Echoes is the franchise's first depicted stage-Stand mechanic — three discrete Acts with separate abilities and separate combat personalities. The mechanic is the structural template for Tusk's four-ACT progression in Steel Ball Run.
- Koichi's age across Diamond Is Unbreakable is fifteen — younger than Josuke and Okuyasu by roughly a year. The shortness and youthfulness are deliberate visual signals of his role as the franchise's audience-perspective character.
- His Japanese voice actor in the 2016 anime is Yuki Kaji, best known outside JoJo for playing Eren Yeager in Attack on Titan. The casting was a deliberate departure from Kaji's more emotionally intense regular register — Koichi requires a more grounded, observational vocal performance.
Frequently Asked Questions
Who is Koichi Hirose?
Koichi Hirose is the audience-perspective character of Diamond Is Unbreakable and the only Stand User in the franchise to recur as a main character across two consecutive Parts. A Morioh middle-school student whose Stand Echoes evolves through three Acts, he serves as Josuke's closest friend across Part 4 and is sent to Italy in Vento Aureo's opening chapters by Jotaro to retrieve a DNA sample from Giorno Giovanna.
What is Echoes?
Echoes is Koichi's three-stage humanoid Stand. ACT 1 projects onomatopoeic text that produces sounds. ACT 2 projects sound effects into targets to produce matching physical sensations (BURN, CRUMBLE, etc.). ACT 3 is a small humanoid Stand that multiplies the gravitational weight of any target it touches — the most-combative form and the one Koichi uses against Yoshikage Kira in the Kawajiri house final battle.
Does Koichi appear in Vento Aureo?
Yes. Jotaro Kujo sends Koichi to Italy in Vento Aureo's opening chapters with instructions to retrieve a DNA sample from Giorno Giovanna — biologically DIO's son via the Joestar bloodline body. The mission is Koichi's most-recurring single-arc appearance outside Diamond Is Unbreakable and the franchise's only depicted recurring-Stand-user-main-character arc across two consecutive Parts.
How tall is Koichi?
Koichi is 157 cm (5'2") — the shortest main Stand User in Diamond Is Unbreakable and one of the shortest across the entire franchise. His shortness and youthfulness are deliberate visual signals of his role as the franchise's audience-perspective character — the small, ordinary Stand User the reader follows through Morioh's supernatural events.