What Japan's large armored cruisers were for

What were the Tsukuba- and Ibuki-class large armored cruisers intended to do?

They supplied reconnaissance, presence, and heavy cruiser combat against likely Russian, German, or possibly American opponents.

Tsukuba and Ibuki supplied the capabilities expected of large armored cruisers around 1905. They could conduct reconnaissance, maintain a naval presence and deal with opposing cruisers. Russian and German ships were likely concerns, with American ships another possibility. Their 12-inch guns added substantial fighting power. The Spanish-American War is cited as a reason to prepare for threats even where a rival's large-cruiser force was limited.