I was with my camera just relaxing, when I heard the tailorbird squeaking unusually, as it does when sunbirds' visit to the shrub also coincides with theirs. But when I saw this one, I was confused. It was not a tailorbird. It was not a sunbird. A Prinia had once visited when I was watching. But this does not look the Prinia on the earlier visit. See the colour of the legs, claws on its feet also. What could this be?
The second picture shows the tailorbird trying to drive away the new visitor. Tailorbirds seem to have 'marked their territory'.
One of the larger Acrocephalus warblers. The one that's common in southern India is Clamorous Reed Warbler Acrocephalus stentoreus. A bit out of its normal habitat (papyrus beds), so I'd suspect it's a recently arrived winter visitor from a bit further north that hasn't found its preferred habitat yet (that's probably why you've not seen one before!).