GS Sailor Eridani
Sailor Pluto can stop time, even though she will die if she does that. If something really bad happened she could jump into the time stream and stop it. She wouldn't though, so I guess it doesn't really matter.
sweatdrop Well to be technical, Setsuna's role is merely to guard the flow of time and stop evil from disrupting its fated balance. She can't really STOP anything from happening... she can do all that she can to prevent it by aiding in the fight but really... she can't necessarily stop it.
In all the cases she's actual done it, the event she prevented was also meant to be stopped... because the survival of Crystal Tokyo has been predetermined and therefore any evil that tries to take away the future is really changing what is fated to be.
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My personal opinion on the strongest of the senshi actually depends on the way you look at strength.
Sheer power- Sailor Saturn. Yes, she can destroy planets and that is why she is so feared and even hated in the pat. Her rise heralds the end of all things. (Although not the case as we've seen)
Strength of body- Sailor Uranus.... someone please try to take down Haruka in a fair fight? You'd fail so pitifully.
Strength of mind- Sailor Jupiter, not much can take away the determination in Makoto. She's by far the most capable of always finding a way.
Strength of heart- Sailor Moon, she really has to be. To be a leader one must be able to defend those they love without regret or hesitance. Usagi looks at everything as though nothing matters and sees the beauty in all things. She heals others with no regard to herself... despite being scared.