I don't like Kimi or his blood line limit either.

No matter what you do with bone calcium, it's brittle. Sorry guys, it's just a fact of being where it is on the periodic table of elements. People are saying "well, it's super hard!" Well, super hard things break really easy. Try a diamond (the hardest substance known) versus a hammer. Well, don't.... give the diamond to me and you can have my word on it. All that matters for "durability" is really tensile strength, and... calcium has none.

Also, as for bone growth, those bones would have to grow from somewhere, which means he'd have to be eating Tums (with Calcium!) non-stop to have that much bone growth potential.

Yeah yeah, it's a story. I'll definitely agree with that. And yes, I know that stories aren't cool unless they bend what could/should be, quite frequently, sometimes.

Having said that, I think it'd be much cooler if he couldn't take his bone swords out, and his bones could break. It would give the story-arc a martyred feel if he were mauling Lee with these bones that were snapping off after having stabbed Lee. Lee'd be staggering around looking like a pin-cushion, Kimi would be reeling from the pain of having all those broken bones, and, and, and... that'd be neat. Actually, would feel a whole lot like the Zabuza-arc end.