How to make beautiful line breaks in Japanese?

I have no experience with Japanese in HTML, but maybe you can use word-break:keep-all;?

According to Mozilla:

keep-all

Word breaks should not be used for Chinese/Japanese/Korean (CJK) text. Non-CJK text behavior is the same as for normal.

div {
  display:inline-block;
  font-size:30px;
  width:100px;
  border:1px solid black;
}
.break {
  word-break:keep-all;
}

<div>寿司が&#x200a;好き&#x200a;です</div>
<div class="break">寿司が&#x200a;好き&#x200a;です</div>