Pikachu are a small species of pokemon which many people find cute, and for this reason have become quite popular as pets, even among people with little interest in pokemon battles. This is an unfortunate fact which leads to many electrocutions, for a Pikachu can be quite dangerous to handle.
Pikachu are a pokemon which store electricity in their cheeks, but this electricity must be released on a semi-regular basis lest the pokemon use powerful electric attacks at random, shocking everything in sight. Typically this is handled by occasionally hooking the rodent up to a special battery which is recharged by its shock, then using the electricity to power the household. Furthermore, they do not only use thundershock to release energy, but also when startled or angry, and they do not have especially forgiving tempers. Many a trainer has been hospitalized or worse when quarreling with their pokemon, some passing away from shock wounds which could have been properly treated were the trainer not embarrassed for how this reflected upon them as a trainer. Moreover there is the issue of weather; Pikachu can seldom be cooped up inside for long, but they are prone to causing nearby people to be electrocuted in rain, and its tail can attract lightning in thunderstorms. Proper care involves the usage of a pokeball in inclement weather, but Pikachu are often reluctant to be so confined. Many inexperienced owners are equally reluctant to use them, fearing it will mark them as pokemon trainers and force them to accept challenges and see their precious Pikachu injured.
Despite this, with a gentle spirit and proper caution, Pikachu can make for excellent pets.