This Pikachu is an Electric-type Pokémon owned by Red.
Red captured Pikachu in Viridian Forest with his Bulbasaur. Immediately after catching him, Red sent him out and allowed Pikachu to have a look around. Pikachu then engaged a Caterpie in battle as a Zapdos flew by.
Later in Johto, Pikachu ran alongside a group of swimming Wooper before climbing a tree and tried to shock them with Thunder Shock. The Wooper were unaffected and knocked him off the tree with Mud Bomb as Lugia flew past.
Pikachu later battled a Vigoroth on the bridge outside the Weather Institute in Hoenn while Latias and Latios watched. Pikachu shocked Vigoroth and slammed it a couple of times, angering it enough for it to accidentally cause the bridge to start falling apart. Pikachu and Vigoroth raced to safety just in time.
In Sinnoh, Pikachu battled a Probopass outside Snowpoint Temple, striking it with Iron Tail before dodging its attempts to crush it or shoot it with its three mini-noses, which were being used independently from the rest of its body. The battle disrupted Regigigas who emerged from the ruins, knocked Probopass away and then unleashed a powerful attack on Pikachu.
In Unova, Pikachu and Red explored the Relic Castle and Pikachu fell through some quick sand into Volcarona's room. Volcarona attacked with Heat Wave but Pikachu used Iron Tail to flip one of the floor tiles up in front of him as a shield. Once Heat Wave ended, Pikachu jumped onto the makeshift shield and lunged towards Volcarona with Volt Tackle, smashing it into the wall. A moment later, Landorus burst out of the ground and lunged at Pikachu.
Along with Red, Pikachu rode in a mining cart inside the Terminus Cave in Kalos whilst fending off a wild Noivern. Pikachu leapt off the cart and landed an Electro Ball. Noivern quickly recovered and flew back towards the cart with Pikachu holding its wing. Pikachu dropped back into the cart and Noivern turned and fired Boomburst but Pikachu's Thunderbolt blasted through the attack and defeated Noivern. After that, Pikachu and Red witnessed Zygarde in its Complete Forme rising into the air.