Starting the day sitting second, Katsuta leapt into an 11.4s rally lead over Hyundai's Esapekka Lappi after a drama-filled stage four, which resulted in Rovanpera and Ott Tanak retiring from the day's action.
Overnight leader and reigning world champion Rovanpera, making a return to the WRC in a part-time programme for Toyota, was the victim of a snowbank. His rival Tanak suffered a similar fate that damaged the radiator on his Hyundai.
The incidents elevated Toyota's Elfyn Evans to third (+13.3s) ahead of M-Sport Ford's Adrien Fourmaux (+18.7s), with road opener Hyundai's Thierry Neuville in fifth (+40.5s). Oliver Solberg led the WRC2 class in sixth overall (1m09.2s).
Crews faced incredibly difficult conditions for the opening stage of the day as fog and drizzle added to the complexity.
Road position was crucial as conditions improved after each car passed through the #42 Brattby (10.76km), renamed this year in honour of the late Craig Breen, who declared himself the "Mayor of Brattby" after posting a record time last year.
Rally leader Rovanpera made the most of starting seventh on the road to win the stage by 3.2s from Hyundai's Lappi and Tanak. The latter faced the challenge of being third on the road.
Rovanpera revealed at the stage end that he struggled to get a good flow behind the wheel, while Lappi, who followed Rovanpera into the stage, survived a brush with a snowbank that dented his confidence.
"There was one corner where I touched a snowbank quite heavily. After that, I maybe drove a bit slow. Maybe that was not a smart idea. I should have used them instead," said Lappi.
Source: Autosport