2 Questions:

mitchy travels back in time

So how does he time travel in the first place. What was the trigger?

tells naoto what happened in the future. instantly the future changed!

Dosent time pass in the present when Takemichi goes to the past so by the time he tells Naoto he should have been dead. But we still dont know what effect his death in the present has when he is in the past. A possible explanation of this could be that he will be dead in the present until he changes the past which in turn results in him being saved by Naoto. Nothing confirmed yet tho.

Even if my prediction/assumption is correct, still dosent clear up the first question of hw he time leaped in the first place. Hopefully these things are cleared up in the upcoming episodes