Mahou Shoujo Ikusei Keikaku: breakdown

A failed experiment results in the death of a renowned mage, prompting widespread grief in the Magical Kingdom. Several months later, the mage's relatives receive correspondence from his representative concerning the inheritance of his property, directing them to a small, unoccupied island where he once maintained a retreat and laboratory. Mana, upon receiving one of these letters, is doubtful but eventually decides to seek out two of her magical-girl friends to join her on the journey.