For this cat, other cats are not company that needs managing; they are the main source of stress in the house, and every shared resource is a place where that stress concentrates. Enrichment therefore starts by subtracting contests, not adding toys: a day in which nothing valued has to be defended, queued for or approached past a rival is already a richer day.
Make Every Basic Resource Genuinely Private
Feed this cat separately, behind a door if necessary, at predictable times, and lift the bowl afterwards so meals never become a guarding post. Provide a litter tray in space the other cats do not control, on a route that does not pass a favourite ambush corner, because a cat who is jumped on the way to the tray will start avoiding the tray, and the household will misread the result as a toilet problem.
Apply the same rule to rest. A window perch, a high shelf and a warm bed inside this cat's secure area, used by no other cat, give the deep, unguarded sleep that cats in tense multi-cat homes often go without. Scratching posts belong in that private set too, since scratching is scent marking as well as nail care, and a post saturated with a rival's scent is not a resource, it is a message.
Solo Play That Needs Nobody Else
Run play sessions with the door closed and the other cats elsewhere, so this cat can chase, pounce and carry on without monitoring the room. Short wand sessions, a kicked toy to wrestle, or treats flicked one at a time to chase across the floor all work, and the session ends with a small meal in the same private space, completing a hunt sequence that belongs entirely to this cat.
Puzzle feeders earn a particular place here: they occupy the mind for twenty unhurried minutes, they cannot be rushed by a bolder cat, and they deliver food in a pattern closer to working for a living than waiting for a bowl. Start with an easy setting the cat solves quickly, because frustration is not enrichment for an already vigilant animal.
Novelty Without a Rival's Scent on It
Rotate toys, boxes and resting fabrics within the private territory every few days, washing or airing items before they return so they do not arrive carrying another cat's smell. A fresh cardboard box with two cut entrances, a paper bag to occupy, or a perch moved to a different window all register as new territory to explore alone.
Add scent and sound interest that involves no other animal: a view of a bird table outside the window, grass grown indoors for chewing, or cardboard scratchers in a new shape. The aim is a day with events in it, spaced across morning and evening, so long stretches are not spent simply watching for the others.
If Tension Is Constant, Change the Map
Where staring, blocking doorways, chasing or fighting is daily rather than occasional, enrichment alone is not the honest answer. Separate zones with their own complete resources, and a gradual, structured reintroduction if you attempt one, protect this cat's welfare better than hoping familiarity will soften feelings. A vet check is also worthwhile when hostility is new, since pain and illness lower a cat's tolerance sharply.
Judge success by this cat's body: sleeping stretched out in the open, playing without glancing at the door, eating at a normal pace. Those are the signs the private day is working.
Recording which toys rotated, which room hosted play, and who ran each session, in KinsLe using Care Teams, keeps the private rota running even on busy days.