The Titanians are invaders from the Titanian Nebula, they have come to Earth to steal its resources and have decided to start their conquest in Japan. Instead of conrolling giant robots they actually transform themselves into giant insects. They also have the ability to take possesion of humans, temporarily turning them into Titanians. One such possesed indivudal can themself possess another who can than take over another, etc, allowing one Titanian to control multuple humans without having to capture each one himself. The first possed human will have super human strength and endurance but this is not shared with the others. The posssed will return to normal (with no memory of how they were used) only after the Titanian who is controlling them is killed. Titanians can fly.
All Titanians look alike when human sized, they wear a black hat, a white mask, black red-lined robe, a black shirt with a big red "T" on it white plants and black shoes (just like their leader). Their true forms however are giant insects. When human sized none of the Titanians (not even their leader) have names, only numbers.. Although there were ten seen at the beginning of episode 18 only 6 transform.
Titanian #1 - the leader of the invasion of Earth (episodes 18-26)
(does not appear in monster forme)
19: 02-18-1973 Titanian #2: Kabutoron: sprays Balloon Bombs out of its mouth, red balloons that explode releasing a toxic gas, can also release the gas directly and on top of its head is giant drill - when it first giant sizes only Kirishima, Goro can see it for what it really is, a space bug, all Shizuka, Gentaro sees is a giant man in a mask and cape and he's not impressed
20: 02-25-1973 Titanian #2: Kabutoron - disguised a villager the human sized Titanian #2 puts up a good fight, Gentaro apparently thinking he's Hongo, Takeshi tries to "Rider Kick" the man, it doesn't work
21: 03-04-1973 Titanian #3 :Kamagyrus: could shoot off its mandibles and spray webbing from its body - lead a team of Titanians disguised as business men trying to be a lethal gas from its inventor
22: 03-11-1973 Titanian #4: Kiri Giron: sprays a toxic gas - takes possesion of a construction worker when he accidently discovers where their secret underground base,then kills the rest of the crew and destroys their equipment all without changing form
23: 03-18-1973 Titanian #5 :Kangarole: sprays acid and breathes fire, flans the flames with its wings - takes possesion of Fujimoni, Noriko in order to kidnap a rocket scientist's secretarym then tells Gentaro and Goro it is the secretary who has been possessed
24: 03-25-1973 Titanian #6: Cockroachaur: fires explosive charges out of its claws, the hole in its stomach is a giant vaccuum - intentionally shows himself, humansized and allows a tracker to be placed on him, in order to lure Gentaro and Goro away from the Tokyo condo the Titanians had just take over as a forward base for their attack on Tokyo, at the same time in Tokyo #7 takes possession of a group of children [apparently the writters forgot which Titanian had the children because they were freed when #6 died but it was #7 who took them over while #6 was out of town]
25: 04-01-1973 Titanian #7: Cricketton & Possessed Iron King: Cricketton fires off explosive charges and shoots off its wrench shapped limbs as missiles - Titanian #7 kidnapped "Tenko" while Gentaro and Goro were destracted by burning dumies of Gentaro & Iron King, her broach has a homing beacon which #7 turns on after tiring her up so she can't turn it off in order to lure them into a trap , Gentaro, Goro and Iron King rescue her but the next morning Goro is possessed and attacks Gentaro, while those two are fighting, #7 attacks Tokyo, at this point the Titanians don't seem to realize they have Iron King under their control but Gentaro doesnt know Goro is Iron King ether after knocking Goro out he planned to take Goro back to headquarters which would have been the smart thing but when the monster attacks Tokyo he stops and ties Goro to a tree instead which was a very foolish thing to do as once Goro awakens he becomes Iron King and joins Cricketton in attacking Tokyo
26: 04-08-1973 Titanian #7: Cricketton, Possessed Iron King - the Japanese military attacks Cricketton and the Possed Iron King, but Titanian #1 orders #7 to retreat while they watch the humans and their former hero battle each other, as dense as ever Gentaro cannot figure out how Iron King got "body jacked" until Iron King runs out of water and Gentaro and "Tenko" find Goro dying of thirst, at last Gentaro understands, Gentaro takes Goro to National Security Organization headquarters where he convinces Dr. Tsushima to remove Goros ability to transform into Iron King, since Iron King has disappeared Titanian #1 sends #7 to attack Tokyo again, Dr. Tsushima's attempt to detransform Goro seems to have killed him, Gentaro goes into battle believeing he's killed his friend, but in fact Goro has so energized that Iron King is more powerful than he's ever been and the Titanian influence has been purged, for the third and final time Iron King defeats a monster without Gentaro's help, the war is no over however as Gentaro sings one last song (clearly prerecorded and lipsychned) the last remaing Titanians land and attack, #8, #9, #10 don't put up much of a fight and are easily taken out, #1 threatens to return with more Titanians but Gentaro follows him into his ship and as the two fight inside it Goro transforms into Iron King one more time, as Gentaro fall out of the space ship Iron King destroys it, thus killing Titanian #1 and ending the threat, then just before Gentaro goes splat Iron King catches him, the end.
With the invasion of the Titanians stopped Japan is finally at peace (as far as Iron King is concerned)