Unfortunately, this Hinoki appears to be in terminal decline or already dead. (Needled evergreens can be functionally dead for some time before finally shedding or browning all foliage.) If the camera color settings are misrepresenting how off-color it looks (to us, it seems paler and duller green than it should be, which is normally a telltale sign it's dying) then you're welcome to send additional photos.

It's hard to determine what caused the initial damage, given how established the plant was. They do not tolerate poorly drained or over-saturated soil, so perhaps a flooding event in the root zone kept the soil too wet for too long. Oxygen depravation from this will kill roots on sensitive plants, and often a root-rotting pathogen sets in and continues root death even once conditions improve. This is not treatable or something from which most plants recover once root loss is extensive.

Was any herbicide used nearby? Some chemical ingredients can be absorbed by tree/shrub roots in the vicinity of application, though such warnings are mentioned in their label usage instructions.

Does any mowing or weed-whacking equipment come near the trunk, where accidental injury occurred? If the Hinoki was experiencing drought stress or overly-wet roots, or even somewhat minor injury from bark cuts, certain wood-boring insects (such as various beetles) tend to target such plants and their activities cause serious and often fatal damage. You'd see small holes, cracks, or sawdust on the main trunk if they were present and a generation of adult beetles had already emerged. (If you remove the plant, you can also split open the trunk to look for signs of tunneling for larvae which have not yet matured.)

Do you know if voles are a problem in the yard? If so, check the base of the trunk for signs of gnawing and bark removal. This girdling kills sapwood vital to the health of the above-ground growth, and too much sapwood loss is fatal. (The only living layer of wood in a trunk or major branch is just underneath the bark; the inner core is naturally already dead. Therefore, damage does not have to penetrate deep into the inner wood in order to be significant.)

Is landscape fabric used under this planting bed, and if so, was it laid close to the trunk? Over time, as trunks expand, these fairly inflexible materials can effectively "strangle" the wood and interrupt water flow into the foliage. They may also impact how well rain and irrigation seeps into the root zone, plus how much oxygen roots have access to.

Miri

Hello Emily,

A soil-borne pathogen won't necessarily threaten other shrubs, in the sense that they are ubiquitous organisms for which eradication is impractical or impossible. They tend to only damage plants when conditions are right for infection - the moisture and temperature conditions are ideal (which will vary by species) and the plant is under stress or otherwise vulnerable. Healthy, vigorously-growing plants are not at greater risk.

The excessive rains from a couple of springs ago could have played a part. If a roof downspout empties in that area, this too could have exacerbated things. Clay soil by itself is not terribly problematic, but its greater ease of compaction and thus poor drainage can be. You can alleviate some of this by adding organic matter (like compost) when planting, and any subsequent mulch topdressings in future years will continue to add organic matter to the soil to improve conditions.

If the site is full sun (6+ hours), there are a number of evergreen or deciduous shrub candidates to replace the Hinoki (too many to list here). If the soil is prone to staying on the damper side, then that will narrow the choices down a bit, but still leave you with several options.

Miri

You're welcome.