Hey there, fellow expat in Japan! It’d help if you were a bit more specific about the types of roads you’d like to ride.
I have lived near Fukuoka, in Nagoya and am now living in Sendai. In each of these places, the roads were quite different. Gravel roads here in Sendai are pretty difficult to come by, and for the most part, riding my bike means road riding on paved surfaces of various quality. If speed weren’t a concern, I’d get a frame with clearance for up to 40 mm tires and stick either a Schwalbe G-One Speed/Allround (35 or 40 mm) on it or one of the fast Gravelkings (38 mm). That should deal handily with everything up to mud or single track.
Whether you’d like the particular frame from Merlin is completely impossible to answer. Gravel bikes on average have a particular geometry which is subtly different from an endurance road bike. And even within each category, there are tons of variations. The Open UP has an endurance road bike geometry, the 3T Exploro is racier and still others are slacker. Where the Merlin Malt slots in, I don’t know, and numbers typically make that pretty hard to tell.
Several members in the Tokyo Cycling Club forum have bought titanium frames to make a comfortable drop bar road bike, and they seem to really love theirs. Lynskey gave an extra 20 % discount to forum members, and their frame prices start at $1,850 before any discounts. Titanium is supposed to be the goldi locks of bike frame material, especially if you prefer a comfy ride. I don’t have any first-hand experience nor are they my cup of tea (I want something racier).
I know this is quite hard in Japan, especially now with the pandemic, but I’d try to test ride as many bikes as I could to find out what you like and don’t like. With the exception of one bike shop, the shops here in Sendai don’t let me test ride anything. And even if they did, it is at least one size too small.
Also, what is your total budget, what kind of gearing do you think you will need and what kind of ride do you want to have?
PS Perhaps the epic Rides of Japan Youtube channel will be of interest to you. He used to have a Mason Bokeh and now owns an Open UP, which he loves.