Saikō-ji belongs to the Jōdo Shinshū Honganji-ha sect founded by Shinran. His teachings of 'salvation of the wicked' and 'Other Power' likely provided the spiritual foundation for founder Shaku Gensei's decision to abandon the sword for the nenbutsu path. The name 'Saikō' (Western Light) signifies the radiance of the Western Pure Land.

The founder Shaku Gensei was a fourth-generation descendant of Sassa Narimasa, the fierce Oda retainer who governed Etchū and is legendary for his midwinter crossing of the Tateyama mountains. After Narimasa was ordered to commit seppuku by Hideyoshi, his descendants left the warrior class. That Gensei founded this temple gives it a unique historical depth as a place of prayer built by the heir of a Sengoku warlord.

The principal image, an Amida Nyorai statue, is attributed to the Heian monk Eshin Sōzu Genshin. Author of the Ōjōyōshū describing hell and paradise in vivid terms, Genshin laid the foundation of Japanese Pure Land devotion. That a statue attributed to him rests in Roppongi testifies to how mid-Heian Pure Land thought lives on in central Tokyo across a thousand years.