The Saviors of Kamigawa card Promise of Bunrei is an enchantment that grants four 1/1 colorless Spirit tokens when one of your creatures dies. The concept behind the card is that the soul of your fallen warrior becomes split into four individual kami -- bunrei -- hence the enchantment represents the promise of those bunrei.
Note that you can see the four spirits splitting out from the soul of the fallen warrior right in Stephen Tappin's art:
Promise of Bunrei art by Stephen Tappin
The strength of the card became apparent during the card's development. There was discussion of having the tokens fly, or making the enchantment's sacrifice optional -- which made the card overpowered. There was also discussion of how powerful the tokens' Spirit creature type was in the Kamigawa block, but R&D decided that interactions with cards like Long-Forgotten Gohei made the Promise of Bunrei strong but not too strong. For more on this card, check out Mike Flores' article on its Constructed applications.