The kanji character for “dai,” or “large,” is said to look like a human being. Perhaps Okuribi is meant to signify the sending of human spirits.
The Okuribi begins quietly, visible from the streets of Kyoto, and ends in the same fashion. However, time flows differently for those at the foot of each of the mountains. Locals gather a month in advance to cut the mountain brush and lay the groundwork. They’ll gather at the temples to chant a sutra. Then, when they receive the cue, they’ll light the fire. The “daimonji” fire begins in the middle, then spreads out to each of its five points.
Why must there be a fire? Because smoke rises to the heavens when a fire is lit. The smoke is said to reach Buddha all the way in the pure lands of Sukhavati. You can burn a “homa” stick beforehand as well; these are wooden sticks with prayers written on them. That way, your prayer may reach Buddha alongside the main bonfire.
You can also climb the “daimonji” mountain; why not take a little hike for a “backstage pass” to see the fire bed?