It's a traditional way to write Japanese Vertically and it's widely used till this day.
Some might suggest to break lines to mimic the vertical writing but it doesn't work.
Here is why. I attached a pic showing the problem.
If I just break each line, some letters' rotation won't be correct.
I've seen this so many times in Hollywood movies trying to show vertical Japanese writing.
Of course you could outline Japanese letters and arrange them vertically but that's too tedious if there are a lot of vertical writings.
Also some Japanese fonts have specifically vertical ones for a design purpose.
This is the big deal breaker for Japanese to use/switch to Affinity products.
I greatly appreciate if the team would consider to add this feature.