Go ahead, Pikachu's partner system is equivalent to an idle elf reuse system. It will open when players reach level 60, and then open one position for every level 10, up to six positions.
Players can put idle elves (not playing) into the position of the little partner system. They can make the on-the-spot lineup get attribute combat power bonus, and they can also make the on-the-spot elves get combined skill bonus. The premise is that the combined skills can be formed between the two elves, and the added Elves will get additional bonus if they are improved.