[FairyKing]

Wasn't there a pattern, at least in post-Decade seasons, of alternating between sci-fi and fantasy sources for the monsters and Rider powers? W had data, OOO had alchemy, Fourze had alien technology, Wizard had literal magic. Gaim sort of broke the pattern by having both interdimensional travel and weird Biblical stuff about the Forbidden Fruit, but then the next three returned to form with Drive having machines and AIs, Ghost having ghosts (duh) and Ex-Aid having video games and computer viruses. So if the pattern continues, I'd expect Build to have some kind of magic or mysticism as his power source.