The Reiss Titan was among the largest monstrosities of the Attack On Titan universe. Towering at a massive 120 meters tall, it was twice as large as the Colossal and perhaps the greatest threat that the heroes faced until their excursion into Marley.
Despite its unprecedented size, Rod Reiss is not invincible, as illustrated through his demise by Historia. By identifying the anime characters capable of stopping him if placed in the Scouts' situation and those who are not, we can better estimate how inexorable the giant actually was despite his mindlessness.
10 Couldn't Stop: Pride's Piercing Attacks Are Weak Against Heat & Sunlight (Fullmetal Alchemist)
Pride's shadows made him an extremely formidable villain given their reach and how easily they can pierce human flesh. However, Selim has a number of shortcomings that would guarantee his defeat.
Not only does his darkness have comparatively lacking striking power (better equipped to kill human enemies rather than to cause widespread destruction, as would be necessary against the Reiss Titan), Pride has a weakness to sunlight and heat. Considering that the monster attacked during the daytime and secretes boiling steam, circumstances counter the homunculus perfectly.
9 Could Stop: Benimaru Has Mobility, Experience, & The Firepower To Put Reiss Down (Fire Force)
Benimaru was the leader of Company Seven and the strongest warrior of the Fire Force series. He was powerful enough to defeat infernal demons through the raw ferocity of his flames, entailing that he should possess the skills necessary to penetrate Reiss' titan skin.
Additionally, the man has incredibly high perseverance and mobility, as illustrated through the defense of his district and investigation of the Holy Sol Temple. Subsequently, he should be able to ignore whatever steam Rod summons to rebuke him with.
8 Couldn't Stop: Edgeshot's Quirk Would Be Worthless Against Rod (My Hero Academia)
Under ordinary circumstances, Edgeshot is more than capable of dispatching titan users. His quirk to fold his body and infiltrate his enemies provides a perfect means of accessing the nape of their necks and destroying them.
However, the Reiss titan secreted so much steam that the Scouts had to cover themselves in water just to remain in its general proximity. Therefore, should the professional hero approach him unprepared - as he would, without prior knowledge of Reiss' abilities - he would be burned alive inside the giant's body and fail to take him out.
7 Could Stop: Escanor Could Obliterate Reiss With A Cruel Sun (Seven Deadly Sins)
Considering that the Reiss titan would attack during the day, Escanor is at a massive advantage. Even before reaching the precipice of his power, he was able to cast Cruel Suns devastating enough to evaporate an entire lake.
Since only a few kegs of explosives were necessary to send Rod's body scattering in all directions, the Lion Sin's inherent might should be more than enough to obliterate his target. He has the durability to afford a point-blank attack if necessary, as proven through his fight against Estarossa.
6 Couldn't Stop: Levi Couldn't Take Out Rod By Himself (Attack On Titan)
Levi is the strongest soldier in Paradis' service and a man who defeated the Beast Titan on a number of occasions. However, he needed help in order to defeat Rod, fleeing behind Eldian walls instead of confronting the monster directly because he knew he was outclassed.
Rod's skin is much harder than a standard titan's and could resist the effects of Ackermann's blades. Moreover, the steam he secretes would deflect thunder spears, eliminating any odds the scout has of defeating him without time to prepare and allies to confer with.
5 Could Stop: Pain Could Destroy His Body With An Almighty Push (Naruto)
While virtually none of Pain's standard tactics would be useful against the Reiss titan, his Almighty Push has had provably devastating results. It decimated nearly the entire village in a single attack, with Nagato retaining enough strength to fight a Sage Mode enhanced Naruto shortly after.
Considering the magnitude of its force, the Akatsuki leader would easily be able to scatter Rod's massive body across the Eldian continent. His only challenge would be to find and destroy the nape of his neck before the giant could reform.
4 Couldn't Stop: Uryu's Weapons Lack Striking Power Even With Prep Time (Bleach)
Uryu's Quincy weapons may have produced decent results against opponents of similar size and anatomy, though they have depressingly low destructive force. Even a concentrated barrage of attacks was not powerful enough to bring down Yammy Llargo - to the contrary, the bruiser ignored the arrows lodged in his skin.
Given Rod's similarly high durability to the Espada's, it follows that Uryu has no hope of bringing him down regardless of the tactics he employs.
3 Could Stop: Esdeath's Time Freeze Would Provide Her An Opportunity To Win (Akame Ga Kill!)
General Esdeath's Imperial Arms allowed her to produce gigantic columns of ice by which to facilitate her attacks. She has used them to mount and slay giants on a number of occasions, as proven through when she was marooned on an island with Tatsumi.
If she creates a pillar and uses it to leap through the air, she would be able to get near Reiss' nape. Once in range, Esdeath would freeze time to prevent steam from buffeting her skin before destroying the monster's weakness and bringing it down.
2 Couldn't Stop: Josuke's Shining Diamond Can't Heal Him From Reiss' Injuries (JoJo's Bizarre Adventure)
Josuke's "Shining Diamond" has decent offensive utility. It was strong enough to break steel (as proven through his battle against Super Fly) and fast enough to deflect bullets (seen in his fight against Keicho Nijimura).
However, neither feat would be sufficient in climbing Rod or destroying his nape. Further, since Josuke's Stand cannot heal him directly, he would be unable to recover from whatever wounds are accrued when battling his overwhelming opponent.
1 Could Stop: Ace Has Enough Experience & Power To Blow Reiss Up (One Piece)
"Fire Fist" Ace's devil fruit allowed him to turn his body into flames and produce absurdly high quantities of heat. It was to such a staggering degree that he could obliterate entire armadas and ignite islands through the force of his attacks.
Considering his unique physiology and unprecedented power, he wouldn't struggle in emulating the effects of the Scouts' explosive kegs and destroying Rod Reiss' body. Considering how little he is affected by steam or physical attacks, the Whitebeard Pirate would win without risking any retaliatory damage.