You don't have to use 2.5 lb line for your entire line (rod tip to hook). I would suggest a slightly heavier line from rod tip to just below your float, then a lighter tippet from there to your hook. That way, when (not if) you have to break the line because it got snagged on the bottom or to save the rod from a fish that is obviously too big, you should lose only the lighter tippet, not your float and certainly not your whole rig.

By the way, the Kurenai works wonderfully as an extra ultra light fly rod. For "fly line" use size 2.5 or size 3 fluorocarbon tenkara line about the length of the rod, then 3-3.5' of 7X tippet. Size 2.5 or 3 tenkara line is equivalent to 10-12# fluorocarbon, but is hi-vis so you can see bites. Nylon is less dense than fluorocarbon, so it won't work nearly as well.