Inspiration
The bard gets inspiration with inspire at level 9, starting at 0. Every kill of your own gives one, up to 5, and one fades every 30 base turns (3 minutes). When empty, the pool stays with you.
Only Inspire spends it: 3 inspiration and nothing else, and with less you cannot sing it. (The lullaby is paid in mana; see Songs.) A virtuoso’s inspire spends none.