Thunderball kills enemies

During the extreme upgrade mission, Katsumi Barlow cannot gain experience from killing monsters, but only kill points.
But this time, things seem to be a little different.
The difference is that it appears on the experience tree.
When Katsumi Barlow killed the first high-level seventh-level monster, he unexpectedly received a prompt from the system.
"System prompt: Congratulations to the player for killing a high-level seventh-level monster. The experience tree seedling gained 50...