A large-growing, nuisance knotweed for sure. Whether or not Japanese knotweed I would like to see more developed leaves before deciding - Bohemian knotweed is often what plants called "Japanese knotweed" really are.

The only plant that comes to mind is Geranium phaeum 'Samobor'. Here is a link that might be useful: Geranium phaeum 'Samobor'

Looks like my autumn fire sedum in the garden. Get orange-reddish flowers that dry to a neat red-brown when finished blooming.

Oenothera fruticosa aka Sundrops. If you prune it back you'll lose the flowers for a while until it grows back but you won't hurt it. Asters have multiple narrow florets, not a few large petals.