Prosopocoilus giraffa keisukei is a spectacular subspecies of the giraffe stag beetle, renowned for its extreme size and elongated, serrated mandibles. Males can reach up to 120 mm in length, placing this beetle among the very largest members of the Lucanidae. Its mandibles—nearly half the body length—are used in powerful combat, where males lift and throw rivals in competition for mates. This dramatic behaviour, combined with its glossy dark exoskeleton and imposing proportions, makes P. g. keisukei one of the most sought‑after stag beetles in the hobby.
 
This subspecies is native to the Lesser Sunda Islands, specifically Flores and Lombok, where it inhabits warm, forested environments. It forms part of a wider complex of Prosopocoilus giraffa subspecies distributed across South and Southeast Asia, each adapted to different islands or regions. Among them, keisukei is consistently recognised as one of the largest forms, with its impressive size setting it apart from relatives such as P. g. giraffa or P. g. daisukei.
 
In captivity, P. g. keisukei is known for its long larval development, with males typically taking 8–12 months and females 5–8 months to reach pupation. The pupal stage lasts around one month, and adults live 4–8 months, depending on conditions. These timings reflect the species’ substantial size and the high nutritional demands of developing larvae. Adults feed on beetle jellies or fruit, while larvae require flake soil, white‑rot wood, or kinshi to achieve full growth.