English (Source)
Enemy buildings can be destroyed by building towers in the blue spots next to the building. After each wave, each tower deals 1 damage to the building, which will give you rewards when it's destroyed.
Japanese Translation
敵の建物は、建物の脇にある青いスポットにタワーを建てることで破壊できます。各ウェーブの後、各タワーは建物に1ダメージを与え、破壊すると報酬が得られます。