Fixing cracks between wall and sloped ceiling

[Mekrel]

Typically for cracks and repairs in plastered walls, I use some Toupret filler that works wonders but I've never tackled something like that as a infrequent amateurs DIYer.

Below you'll see the poor repair job the builders of the flat attempted. I'm guessing some plasterboard tape (spanning both the wall and ceiling) under the Toupret filler? Is the paper stuff or fibreglass mesh stuff better?

 

[Mercenary Keyboard Warrior]

Has it got movement?
Looks like a stair or something?

 

[Mekrel]

Has it got movement?
Looks like a stair or something?

It's just a corner of the master bedroom, in normal situations it wouldn't have much movement but the building is timber frame and there's lots of movement in general. Especially as to the right of the picture, the wall in question joins to a french door that creates movement when opening and closing.

 

[NickK]

Probably a flexible chaulk as a filler however if you're getting movement with doors opening and closing something may need fixing/stabilising first.