How to increase CTR and conversion rates on Google UAC campaigns?

A CTR of 3-5% is not bad in my opinion. Why do you think this is bad?

I assume that your creatives are good. If you are not sure, then share them with us. Although I have to say that I will not understand Japanese. 

Here are 2 tips that have made a big difference for us:

• Do ASO first and try to do a really good job here! On the other hand, users will not convert and the algorithm will have a hard time finding matching keywords. Above all, create good images and use keywords in the images as well. The feature graphics is also very important. 
• Use different ad groups for different keywords. Use these keywords again in your texts etc. We always have one general and several specific ad groups.