Wireless　sensor　networks　that　enable　advanced　internet　of　things　(IoT)　applications　have　experienced　significant　development.　However,　low-power　electronics　are　limited　by　battery　lifetime.　Energy　harvesting　presents　a　solution　for　self-powered　technologies.　Vibration-based　energy　harvesting　technology　is　one　of　the　effective　approaches　to　convert　ambient　mechanical　energy　into　electrical　energy.　Various　dynamic　oscillating　systems　have　been　proposed　to　investigate　the　effectiveness　of　energizing　low-power　electronic　sensor　devices　for　supporting　various　IoT　applications　across　engineering　disciplines.　Phononic　crystal　structures　have　been　implemented　in　vibrational　energy　harvesters　due　to　their　unique　bandgap　and　wave　propagation　properties.　This　work　proposes　a　Rubik＇s　cube-inspired　defective-state　locally　resonant　three-dimensional　(3D)　phononic　crystal　with　a　5　x　5　x　5　perfect　supercell　that　contains　3D　piezoelectric　energy　harvesting　units.　The　advantage　of　defect-induced　energy　localization　is　utilized　to　harness　vibrational　energy.　The　3D　piezoelectric　energy　harvesting　units　are　constructed　by　the　buckling-driven　assembling　principle.　Adapting　to　the　low-frequency　and　broadband　characteristics　of　ambient　vibration　sources,　soft　silicone　gel　is　used　to　encapsulate　the　buckled　3D　piezoelectric　units,　which　are　embedded　in　the　3D　cubic　phononic　crystal　to　assemble　an　entire　system.　The　energy　harvesting　performance　of　various　defective　layouts　and　their　defect　modes　is　discussed.　The　results　demonstrate　that　the　harvester　functions　well　under　multidirectional,　multimodal,　and　low-frequency　conditions.　The　proposed　methodology　also　offers　a　new　perspective　on　vibrational　energy　harvesters　for　defective　phononic　crystals　with　superior　working　performance.