Siren Builder is the personal emergency mecha of BoukenSilver (Eiji Takaoka), the sixth warrior of GoGo Sentai Boukenger. Its name gives away the concept: the „Kinkyu GoGo Gattai" – the Emergency GoGo Combination – merges three rescue vehicles, GoGo Fire (fire engine), GoGo Aider (ambulance) and GoGo Police (patrol car), into one stocky, powerhouse robot. It is driven by the Neo-Parallel Engine, one of the coveted „Precious" artifacts at the heart of the series.

In the combination, the bulky GoGo Fire forms the head, torso and legs, while GoGo Aider and GoGo Police become the two arms. Its signature trick is the „Jack Up" mechanism: at Eiji's command the legs formed from GoGo Fire extend or retract, letting Siren Builder dodge attacks or leap clear. Up close it unleashes the „Builder Crash," a flurry of rapid punches, while its finisher is the „Triple Liquid Bomber," firing a barrage of heavy water-energy rounds through GoGo Fire's high-pressure cannons.

Compact as it looks on its own, Siren Builder is also a team player: its arm components (GoGo Aider and GoGo Police) can dock onto the Ultimate DaiBouken – the fusion of DaiBouken and DaiTanken – and replace its arms. Mass mergers like this earned the Boukenger the record for most combined mecha (ten as standard, and even twelve in a bonus video).

The DX toy was released by Bandai in Japan in 2006 and reproduces the full triple gattai along with the spring-loaded „Jack Up" leg gimmick. A key note for collectors: the Western counterpart, the Flash Point Megazord piloted by Mercury Ranger Tyzonn in Power Rangers Operation Overdrive, was never released as a toy by Bandai America. That makes the Japanese DX Siren Builder the only way to actually put this mecha on your shelf.