Regen-inf troops were members of the lesser species who were biologically modified by the Great Houses to fight in the War in Heaven. Like the Third Wave, regen-inf were given the ability to regenerate into bodies with built-in weapons. The name was a contraction of the words "regeneration" and "infantry".

While some regen-inf kept humanoid forms, most attained gigantic bodies which were "not even remotely recognisable" as living things. (PROSE: The Book of the War) As time progressed, they would build up layers of "high-technology scar tissue": (PROSE: Dead Romance) thick ablative armour with microscopic torpedo tubes as pores. (PROSE: The Book of the War) Christine Summerfield described one regen-inf soldier as looking like a knight in armour with tank parts for limbs. (PROSE: Dead Romance)

Regen-inf soldiers were also mentally changed to fight in the War. They were given time-awareness and some of their brain structures became dimensionally extruded. Many advanced regen-inf had psychological or even physical self-destruct protocols implanted through briefings; some displayed physical responses to the conditioning, like stigmata and death's-head imprints on the skin. (PROSE: The Book of the War)

Cwej Magnus (right), an example of a regen-inf soldier. (PROSE: The Book of the War)

The Great Houses began using regen-inf in the 4th year of the War (PROSE: The Book of the War)

Emiousha worried about being reprocessed as regen-inf biomass. (PROSE: Against Nature)

One regen-inf soldier impregnated a woman in 14th century Devon; their child absorbed the regen-inf protocols and was born with scaled skin and physical deformities. (PROSE: The Book of the War)

Father Kreiner collected the severed heads of several members of the "lesser races" who been genetically modified by the High Council to have Time Lord-like abilities for use in the War. (PROSE: Interference - Book One)

House Mirraflex once experimented with regen-inf to create the weurmoths. (PROSE: The Book of the War)

A regen-inf honour guard was stationed at the Hall of Autophagic Weaponry to protect the Dry Vineyard. (PROSE: We Are the Enemy)

In the City of the Saved, regen-inf soldiers were politically represented by House Halfling. Verrifant, a former regen-inf, served as Lord Mayor of the City of the Saved for a couple years. Some regen-inf lived in the Ghetto of the Damned. (PROSE: The Book of the War)