These are all short but worthwhile reads for anyone who likes Bleach's cast. They can be read after finishing the Arrancar arc and provide additional details on some of its characters. "Not be, but be" tells Ulquiorra's backstory and gives more insight on his mindset/worldview. Definitely enhances his fight with Ichigo when you realize how nihilistic his life has been and why he would be so surprised by Ichigo and Orihime's enduring sense of hope. "Nestle to Night" is a small epilogue to the Arrancar arc. It explains how Harribel survived and why she decided to become the ruler of Hueco Mundo, and even gives somecharacterization to Yammy's dog. Got surprisingly emotional toward the end.

Finally there's a brief conversation between Kira and Rangiku surrounding Gin's death. Not a whole lot of plot revelations here compared to the other stories, but it's a nice interaction and showcases some sides of Gin that we didn't get to see in the manga (e.g. what he was like in casual settings).

On the whole, these are neat supplementary stories, though given their brevity you shouldn't expect any huge impacts to the main plot from them.