*Has an anuerism cuased by the number of uneducated noobs*
*Recovers from anuerism eventually*
*Meditates*
*Posts*
Plusle and Minun are NOTHING like Pikachu OR EVEN PICHU.
The way Plusle and Minun work is like a battery. They help each other out with certain tasks, usually requiring electrical power. Power flows from the Plus pokemon Plusle to the Minus Pokemon Minun, thus increasing Minun's electrical power. Conversely, Minun can choose to give power to Plusle, increasing the Positive electrical power. Both easily develop a strong sense of teamwork and synchronization, and are all the better when one is even close to the other.
The benefits of teamwork are universal, but are most pronounciated with the incarnations of polaric Positive and Negative working together for the same cause.
What do you get if you gather a bunch of Pikachu/Pichu in the same spot? Just a random of thunderstorm of chaos, and usually somebody gets hurt, in the case of Pichu, especially. Harnessing pure electricity, both positive and negative, all within one being, one life force, it can be chaotic, and hard to control for one so young: ispo ergo Pichu.
As he grows and develops, he learns to harness this electrical gift of his, although he recives no polar benefit and only the trait of static. As electrical powers become easier for an older Pichu, he grows, develops, and overall, evolves. He reaches the stage of his life Pikachu.
Now, Pikachu represents your basic knowledge of control of power. He can harness it without hurting himself much anymore, but it is still contained: limited. A Pikachu may choose not to immediately break the limit, and instead, work about manipulating it. That being said, the border, or limit of all that electrical power from being set free is the now still timid Pikachu himself. So with great skill in manipulating his limit, his body, he learns all the speed attacks that most electric types are notorious for. When fate chooses to intervene, and two magnetic lay lines form a nexus of power, a Pikachu may be given the opportunity to make a one-way decision, for at that location, the Pikachu comes across a Thunderstone.
The Thunderstone offers itself to break Pikachu's limit, and unleash all the monstrous electircity within, to unchain any restraints of shyness the Pikachu once had; it offers the Pikachu the chance at a limit break, an evolution, a chance to be the Thunderstorm unleashed: the chance to become a Raichu.
There's two poetic stories for you so you can HOPEFULLY know the difference between the growth of a Pichu/Pikachu/Raichu, and the teamwork of a Plusle and his buddy Minun.
Take note the above are just stories and are used mainly to contrast Plusle & Minun, and Pichu, Pikachu, and Raichu. Some of the stuff was made up on the spot, but the general idea of the contrast stands true.