That is a ladybird larvae and it’s not killing your box! It’s a great predator to have in your garden as they eat greenfly, blackfly and lots of other small pests that attack our tender plants. The box tree moth caterpillar is difficult to spot and as I’m unable to attach an image to this answer have added a picture of one to my photo’s so you know what your looking for. Hope this helps.

It is definitely a ladybird juvenile and is a really good guy. it will eat any small insects that are on you box plants. Including the first stage box moth caterpillar.

Could it be box blight as suggested when you asked this before?

the presence of the ladybird larva is just a coincidence, your shrubs clearly have box blight which is what is causing the dmage.

As the answers in your previous post have said it is box blight, and as the above comments say this is a ladybird larva. Do not kill it, it is not harming your box plant at all.