Jinpei, designated G-4 and codenamed "Jinpei the Swallow," serves as the reconnaissance expert in his team. He is the youngest member, estimated at 10-11 years old during the original series and explicitly 10 in the OVA. His early life remains largely unknown; Jun discovered him as a toddler in the Jupiter Mountains and brought him to the Shirayuki Orphanage. Raised together there, they formed a strong sibling bond. Dr. Nambu later recruited them, with Jun insisting on joining to stay with Jinpei. An implication exists that Jinpei might be the lost son of the Jupiter Ninja Clan's sensei, though unexplored. At the orphanage, he was known for playful pranks and popularity among other children due to his agility. His civilian look typically features an orange-and-yellow T-shirt marked "4" with blue-and-white striped bellbottom pants. Sequel series update this to a crew-neck "4" shirt, cap, blue jeans, and suspenders. His primary battle uniform, the Swallow-themed Bird Style, is predominantly yellow with red gloves and boots, a dark blue cape (teal-lined), and a blue helmet with a yellow visor. The OVA redesign gives him a beanie and sweatshirt for civilian wear, while his Bird Style shifts to primarily red with yellow accents and a purple cape. Concept art for the cancelled Imagi film explored variations like a gold uniform with red trim and civilian outfits featuring vests, jeans, and sometimes goggles. Personality-wise, Jinpei exhibits typical childlike cheerfulness and excitability, coupled with mischievous tendencies. Despite this, he demonstrates responsibility by assisting Jun in operating Snack J and supporting teammates. He functions as the team's "idea man," often providing comic relief alongside Ryu. His interests include card games and drawing, though he dislikes mathematics and homework, subjects overseen by Dr. Nambu and sometimes taught by Ken and Joe. Key relationships define him: his deep bond with Jun as her adoptive brother manifests in helping at her snack bar and teasing her about Ken. He respects Ken as a leader and brother figure, addressing him informally as "Aniki," while persistently attempting to collect Ken's unpaid snack bar tab. Jinpei's combat style emphasizes stealth and incapacitation, leveraging his small stature. His signature weapons evolve: the original series features American Clackers (bolas for restraint), Gatchaman II introduces the Rebound Ball (a super-ball projectile launched from a mitt), and Fighter incorporates the Swallow Top (a spinning top on a yo-yo string). The OVA equips him with an unnamed hacking device featuring a collapsible screen and gamepad interface, transmitting data to his helmet visor. His personal mecha includes the Swallow Helico, a VTOL reconnaissance craft, and in Fighter, the Gatcha Four tank forms part of the Gatcha Spartan's wings and thrusters. International adaptations significantly alter him. The South Korean dub "Eagle 5 Brothers" renames him Cheol (later Ppyeong in sequels). The US "Battle of the Planets" rebrands him as Keyop, depicted as a genetically engineered child with a speech impediment involving stutters and electronic sounds, attributed to "cerebonic implants." This stemmed from a producer's desire for a comedic voice; uncut dubs confirmed Jinpei's dialogue lacked excessive rudeness. Early concepts for Keyop considered an alien origin or android nature. Beyond the core series, Jinpei appears in cameo roles within the "Yatterman" TV special and episode 24, depicted alongside his team and riding on Ryu's shoulders. He features in "Time Bokan: Royal Revival" during a restaurant scene and briefly in a battle sequence before departing due to boredom over lack of dialogue. He also has an uncredited speaking role in the "Wonderful Tatsunoko Land" special.