kindling fire
熾 centers on fire that is being built up or intensified: kindling a flame, making it blaze, or something burning vigorously.
熾 combines 火 (fire) with 戠, which likely contributes the sound and may relate to a blazing or intense quality. The exact historical development of 戠 is uncertain.
The left side is fire 火, and the right side 戠 looks like a complex arrangement with a weapon 戈 and something standing 立. Picture using a spear to stir up a fire until it blazes: kindling a strong flame.
For シ, imagine a single spark (シ sounds like 'she' in English) that kindles a huge fire. She -> シ, and that one spark starts the blaze.
fierce (fight, competition, etc.); severe; hot; hard; bitter; keen; cutthroat
to be kindled (fire); to be made
to build (a fire); to make; to start; to light
to catch fire (of charcoal); to start burning; to burn away; to burn merrily
seraph
glowing ember (either red hot charcoal or the glowing remains of burnt firewood); live charcoal
intense heat
vigor (like leaping flames); liveliness