Plusle and Miniun

Minun (the little blue one with - signs on his cheeks)
Name: Nubo (from "cloud" of friendly negativity, or "Minus" affectionate, but Nubo sounds cute and it suits him with his worried little face).
Appearance: Just as round and baby-like as his brother, but with bright blue ears and a tail shaped like a minus sign. His cheeks have large, prominent minus signs (like in the photo, with that light minus sign). His eyes are a little bigger and more expressive, always with a look that says, "Oh no, what if something bad happens?" His fur is softer and seems to shine less than Plusle's, but when he's scared or shy, he releases soft blue sparkles like fireflies. He wags his tail slowly, as if he's thinking.
Personality: He's the more cautious and sensitive of the two. He's always a little worried about everything ("What if it rains? What if we get lost?"), but that makes him incredibly loving and attentive. He loves to snuggle up to Chispa to feel safe, and when his brother gets too excited, Nubo gently reins him in with a soft "minu-minu..." to keep him from getting into trouble. He's the one who gives the longest and most comforting hugs, and although he seems like the "negative" one, he's actually the one who cares most about others. When something goes well, his face goes from a frown to a huge, shy smile, and he releases little sparks of relief.

Plusle (the little red one with ears and a tail shaped like a +)
Name: Sparky (or "Sparky" if you want something in English, but Sparky suits him perfectly because of how energetic he is).
Appearance: It's a super round, chubby little yellow bun with big, red ears that look like cheerleader pom-poms. Its cheeks have clearly defined plus signs in light blue (or red, depending on the light), and its tail ends in a giant plus sign that it's constantly waving as if it's clapping. Its eyes are huge and bright, always with a "come on, everything's going to be great!" expression. When it gets excited, its fur crackles with tiny, harmless red sparks that look like mini fireworks.
Personality: He's the classic hyperactive optimist of the duo. Always the first to cheer, he jumps around everywhere, making "plus-plus!" noises to motivate his little brother. He's brave (or at least he tries to be), protective, and a bit bossy, like, "Come on, Minun, don't worry, I'll take care of you!" He loves giving big hugs (tail and all), and if he sees something's wrong, he'll start throwing sparklers to lift everyone's spirits. A little clumsy sometimes, but his heart is pure positivity.

Bipedal Pokémon similar to mice. They speak, but not much; they only say their names and basic words like "milk," "mama," and "hungry."