The itinerary lasts 1day 6hrs 15min, and has 3 steps, and it will cost 112 euros minimum.

Rennes - Paris
The step from Rennes to Paris lasts 1hrs 30min. You'll travel in a high speed train.

Paris - Berlin
Take the train from Paris Gare de l'Est at 7:12pm, arriving at Berlin Central Station at 9:16am the following morning.
The step from Paris to Berlin lasts 13hrs 15min. You'll travel in a Nightjet operated by ÖBB.
On board, you'll have access to: Drinks and snacks.
You can find tickets from 64.9 euros.

Berlin - Stockholm
Take the train to Berlin at 6:34 p.m. to arrive in the Swedish capital at 9:55 a.m. the next morning!
The step from Berlin to Stockholm lasts 15hrs 30min. You'll travel in a EuroNight operated by SJ.
You can find tickets from 48 euros.