All Runes apply to only that character. USE the red rune.

give it to a tank since every rune only applies to the ninja it is placed in

You should plan out what rune you want on which character up front. Life recovery is useful for tank and healer mostly, it can be more useful than some of the secondary stat like crit, injury etc on tank/healer considering the fact that they don't attack much (thou those do also protect against enemy crit etc but only defensive is less valuable than offensive AND defensive on your offensive chars)

I personally would only use a rune of the types that I "planned" to use or a rune that is at least 2 color tier higher than a low-importance planned rune. In this case, for example, if I didn't plan on using life recovery, I would still replace a purple or below crit/injury etc rune with it simply because it will provide sufficient extra raw power to be good enough. But I will NOT replace a attack/ninjutsu rune on one of my attacker with it because those are of higher importance.

Currently, as part of my "plan" include init rune on my attack starters which I haven't been able to buy yet, any unplanned high rarity rune would take those spots until i can actually get the init ones.