The '25 worlds' here means 'three realms and twenty-five forms of existence' in Buddhism which is a thought that there are 25 worlds from heaven to hell (it is considered that there are 14 forms in Yokkai (the realm of desire), 7 forms in Shikikai (the realm of form) and 4 forms in Mushikikai (the realm of non-form).
ここで言う「25の世界」とは、仏教で言う「三界二十五有（う）」のことで、天上界から地獄まで25の世界があるという考えである（欲界に十四有、色界に七有、無色界に四有があるとされる）。