Am I a good candidate for masseter Botox and HIFU for slimmer face? (photos)

Botox can certainly be used to reduce the width of the masseter area, but there are perhaps other issues that you may also want to consider.  You may want to arrange a consultation with a highly regarded plastic surgeon to see all your options, and then make a choice.

Yes, Botox combined with HIFU and radiofrequency treatments can slim the masseter. Botox results resolve in 3-4 months. I recommend getting a formal evaluation with a cosmetic dermatologist. Best, Dr. Emer

Botox combined with HIFU can be used to slim the masseter. Botox results resolve in 3-4 months. I suggest getting a consultation with a cosmetic dermatologist to go over your desired results. Hope this helps.

I frequently use Botox in my asian patients to reduce the bulkier masseter muscles in the back of the jaw to create a V-line shape. The procedure is quick and painless due to numbing cream and the fact that the skin and fat in the back of the jaw is no where near as sensitive as the forehead or eyes where most people get Botox normally. Hifu is better for reducing fat and skin tightening. It may cause some improvement but will not be as dramatic in your case as you are young and still have good tight quality skin. There are other options as well but the best treatment plan is decided after a thorough skin and face examination. Hope this helps!Johnson C. Lee, MD
Board-Certified Plastic Surgeon
IG: @drjohnsonlee

Both Botox and HIFU would help acheive a slimmer face.  Botox or other neurotoxins typically last 3-4 months so you will require repeat treatments for maintenance.  HIFU or Ulthera will help lift and tighten the skin.  In general, the earlier this is started, the better the results.  I typically recommend once a year Ulthera treatments.  Consult with a cosmetic dermatologist for proper evaluation and recommendations.

You have a beautiful Asian face. If you treat your face with a device such as Ulrhera or hifu, it will significantly diminished the amount of fat in your face and age you so much so that you may be very, very unhappy. I would definitely not recommend that to someone like yourself. There appears to be a hollow close to the lower eyelid and that may need to be addressed but needs to be further evaluated in person as the photograph does not show it well. I would recommend seeing a plastic surgeon like myself to see if it needs treatment. Good luck from New York City

While, Hifu is truly a remarkable breakthrough in technology, a non-invasive alternative to a surgical face lift, and a FDA approved treatment with a specific intent for improvement of lines and wrinkles on the face and décolleté, it does depend on the desired "slim look" you're going for. 
From your pictures, I can see you where you may want a tighter look around your cheek bone area giving you the "lifting effect". If so, then you may want to consider juvederm voluma. It's also a non-surgical filler and would give you the desired "lift" you may be looking for. Voluma is a long lasting  FDA approved facial filler, lasting up to 2 years or more. In fact, Voluma is the ONLY hyaluronic acid filler approved by the FDA to specifically contour and volumize the midface. Other fillers typically have a life cycle of between 6-9 months.
All are painless and considering your options, and you may or may not need a single session. The doctor you go to would have to determine that for you. 

Botox to the jawline, masseter region, can help slim the area. Lasts 2.5-4 months typically.Choose an expert. Best. Dr Brecht Seattle, Wa

It depends on what you want to achieve.  You don't have the typical round face that we do masseter reduction for.  I would strongly encourage you to do Botox first to see if you like the results.  While HIFU can be helpful, direct RF to the masseters is much more predictable  I would wait on this to see how you like the effect with Botox.  Seek out a consultation with a board-certified surgeon.  Best wishes.