Hiro meets himself.
In the context of Heroes, a paradox is a situation created by time travel which is logically inconsistent. The classic example is traveling back in time and killing your own father before your conception, thereby preventing your own birth: if you were never born, how could you go back to prevent your birth?
Hiro Nakamura meets Charlie Andrews at the Burnt Toast Diner in Midland, TX. The two become friends quickly, but Sylar kills Charlie while Hiro is visiting the restroom. Hiro decides to go back in time to prevent the murder.
When Hiro seems to be on the verge of taking Charlie on a trip that will keep her from being present at the diner on the date of her murder, he suddenly and unwillingly moves forward in time. Although he tries repeatedly to go back and save her, he is unable to do so.
Future Hiro traveled five years into his past to contact Peter Petrelli, hoping that Peter would save Claire Bennet from Sylar and thereby change history. Although Peter did prevent Sylar from killing Claire, Future Hiro did not perceive any change in his own time; the circumstances that caused him to go into the past did not change.
In order to prevent a paradox by his past self never having to go back in time and thus never fall in love with Charlie, Hiro convinces his own past self to travel through time to save Charlie telling him his mission is now to "save the waitress." This attempt works as shown when Hiro shows up again in Charlie's birthday picture.
When Tommy Clark considers going back in time to locate his sister at a point in time he knows she'll be at, his mother tells him not to because changing the past is "a dangerous game" according to Hiro, referring to Tommy's ability to cause a paradox by changing things.
In the novel Saving Charlie, Hiro accidentally talks to himself on the phone, and isn't sure if he was going to breach the space-time continuum. Hiro says that this is the problem with time travel, that there were so many theories about wormholes and parallel chronologies and paradoxical incongruities. (Chapter 7)
- Charlie was still murdered by Sylar at the diner, but certain historical details changed. For instance, Hiro appeared in a photograph of Charlie's birthday party on the wall, which he did not appear in before going back in time. The incident suggests that Hiro cannot use his space-time manipulation powers to cause a paradox; he could not eliminate his original reason for going back in time.
- From Future Hiro's perspective, keeping Sylar from murdering Claire (Homecoming) should have significantly altered history, but it didn't. Future Hiro still needed a reason to visit the past; otherwise a paradox would occur.
- From a story-telling standpoint, establishing this limit on Hiro's powers helps sustain suspense, as it keeps Hiro from going back in time to reverse every possible setback.
- "Present" Hiro visiting the future may not have the same limitations as Future Hiro does when visiting the past; if Hiro takes action in his native time to alter future events, he may be able to succeed. Future Peter's request to Present Peter seems to support this interpretation.
- Despite Hiro's failure to save Charlie the first time, he manages to save her with a second try without causing a paradox, but is very careful to prevent one or too many changes to the timeline.