Philos is the shared home planet of Xavier and Sylus, establishing an implicit axis between their routes. Xavier was raised as Crown Prince of Philos — the son of the King, trained at Astra Knyght Academy, destined for the Gladius Ceremony. When he discovered that the energy powering Philos was generated by feeding humans to an artificial core, he abandoned his throne and used the Backtrackers' time-travel mission to travel to Earth. Sylus, catalogued HDS-7213, rejected Philos's prohibition on emotion and desire, became the planet's most dangerous fugitive, escaped the space-time prison Tartarus — the only person ever confirmed to have done so — and fled to Earth to 'embrace living.' Neither operates within Philos's current political structure. The To Our Yesterday main story arc (January 2026) brings the Philos backstory into the foreground of Xavier's route. The chapter 'Duel in Linkon' suggests Xavier and Sylus's shared Philosian origins produce a direct confrontation in the present day.