The best replacement for gackt is arashi.

The best alternatives to gackt are rated as following:
★★★★★  arashi
★★★  matsumoto
★★  tm revolution
★★  klaha
★★  hyde
★  miyavi
  ayumi hamasaki
  yoshiki

Your alternative for gackt is not listed? Suggest!
Speaking about gackt, one probably shouldn't forget about hyde.

Other search terms related to gackt and their ratings are:
★★★★★ hyde
★★★★ malice mizer
You have in mind a companion for gackt and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of gackt in all years. Click on graph for more.
gackt
arashi
matsumoto