Soichiro Ichinose is the father of Subaru and Isuzu Ichinose, serving as a leading developer of mobile weapons. His most notable creation is the Durandal mecha, reflecting significant contributions to military technology within the series' universe. During the second season's events, he re-emerges to intervene directly in the conflict between his sons. This involvement includes designing the upgraded Neo Durandal specifically for Subaru, featuring enhanced capabilities and amenities like reclining seats. This technological contribution influences battles between the Earth Union and the People of Metus factions.

His familial relationships are complex, particularly regarding his role in the estrangement and rivalry between Subaru and Isuzu. Narrative developments explore his connection to their conflict, positioning him as a figure whose past decisions shape the brothers' present dynamics. The manga arc "LOVE OF FATHER" further contextualizes his paternal relationships and background.

Physically, Soichiro Ichinose is portrayed with gray hair and gray eyes consistently across appearances, reflecting an older, senior character design. His narrative function extends beyond familial ties into the broader war conflict, where his technological innovations and strategic decisions impact both factions. His presence contributes to plot developments involving factional warfare and mecha upgrades.