Honestly, Japanese idol music fucking sucks, or is just very very bland, because like everything else in Japan it's made for Japanese tastes, and japanese taste alone because they have a big enough market. A common milestone for any Korean group is to start making japanese language releases and promoting there because it opens up a potential fanbase of millions, and you go from playing concerts for 5,000 to 50,000.
There are a few notable exceptions but the music is usually stripped of any edge or experimental qualities and made really bland or cutesy, because that's what they want there. Girls Generation is the only group I can think of where their Japanese albums are actually basically superior in quality. There are K-Jpop releases I like from a number of acts but it's often an acquired taste. The homegrown stuff sucks and is just another thing to highlight that Japan is a literally dying country that hasn't been on the cutting edge of anything since the early 2000s, just stagnating and coasting on their achievements of the past millennia as they drift further into irrelevancy, steadily being eclipsed in soft power by the country backwaters they used to bully and torture for decades.
