Purah's Diary is an item from The Legend of Zelda: Breath of the Wild. Link can find Purah's Diary inside Purah's Room at the top of the Hateno Ancient Tech Lab after speaking to Purah during the "Locked Mementos" Quest. If Link visits Purah's room before the quest, the diary will be missing. Interestingly, Purah mentions the diary herself and during her first meeting with Link and even suggests he read it to learn story about how she ended up in a six year old body, despite insisting he shouldn't read it. If Link does read it, Purah will know and will call him on it when he speaks to her again. If Link admits he read it she commends him for his honesty. If Link lies, she will reveal she knows he is a liar. Regardless of his answers, Purah will threaten to punish him and proceed to seemingly use the Guidance Stone to delete all Runes from his Sheikah Slate and tell him to take a look, before revealing she had not deleted his runes and was simply playing a mean joke on him using her Guidance Stone impersonation.
The diary provides information on Purah's activities during the Age of Burning Fields and how she ended up in a six year old body due to an experimental de-ageing rune that went to far.
"Research diary for anti-aging rune. CLASSIFIED! For Purah´s eyes only!"
Work has finally begun on my anti-aging rune. If all goes to plan, I believe it will effectively reverse the aging process. This technology will enable us to make retired warriors young again, thereby strengthening the Hyrulean army. When Calamity Ganon inevitably returns, we'll be ready. Our offense will be solid, and our defense impenetrable. The need for this tech pains me, but I truly hope to use it to attain everlasting peace for all."
The beta version of my anti-aging rune is complete. I have already added it to the Sheikah Slate I made for myself. Since I am to be the test subject of this experiment, Symin booted up the rune and directed its rays at my body. After 20 seconds of exposure, I felt extreme fatigue and broke into a fever, forcing us to cease the experiment. Unable to stay awake, I went to bed immediately. Tomorrow I will try to figure out what went awry."
"Anti-Aging Experimental Trial Day 2
My extreme full-body fatigue has slightly improved, for which I am grateful. Still, I do not recognize the face in my mirror. My hair is thick again and floor-length. My wrinkles, once deep as trenches, have vanished without a trace. It seems the anti-aging effect works. However, I did not expect the reversal to happen so frighteningly fast. This morning I kicked Symin awake and had him run a full physical exam on me. My height, weight, vision, bone density, heart, blood… We tested everything we could, pushing our facility to its limit. Our discoveries were startling. My results were typical of a Sheikah woman in her early 50s. In other words, I reversed my age by more than 70 years in a single night. I can only hope I do not awaken to find I have the body of a newborn baby…"
"Anti-Aging Experimental Trial Day 3
I awoke with an abundance of energy. It has been decades since I slept so well. Upon waking, I immediately checked the mirror, only to be greeted by a youthful version of myself. According to Symin's examination, I have the body of a Sheikah woman in her 30s. Thirty years old… I was around that age when I was first able to continue my research following the Great Calamity. The first thing I did was try to figure out how to expand the functionality of the Sheikah Sensor. I was around 80 years old when that expansion was completed. I intend to bequeath this tech to our sleeping hero. I hope to the gods that he will be able to assist in the destruction of the Calamity that swallowed our Princess Zelda whole."
"Anti-Aging Experimental Trial Day 4
After today´s routine physical, the results show that I have the body of a Sheikah woman in her 20s. I haven't felt this good in a century! This is all taking me back to when the Great Calamity happened… Ganon had been dormant for 10,000 years. Perhaps his power had been building all that time. The slaughter that followed was arbitrary and merciless. The destruction complete. We lost everything… Hyrule Castle, Princess Zelda… Well, perhaps not everything was lost. A youth named Link was brought to me a hundred years ago, covered in wounds and on death´s doorstep. Link… So young, yet so courageous. He was the youngest knight to have ever been appointed to the Imperial Guard at Hyrule Castle. He was also a gifted swordsman who was selected as captain of Princess Zelda's personal guard. I thought his skills would be enough to defeat Ganon in glorious fashion… Since ancient times, the royal family of Hyrule and us Sheikah researchers have had a strong bond. Their plan is our own. We took the swordsman and the Sheikah Slate Princess Zelda left behind to the Shrine of Resurrection. Although the Slumber of Restoration had not been fully tested, we decided to put the swordsman under to save his life. It was the best we could do…"
"Anti-Aging Experimental Trial Day 5
I awoke to something horrifying… a scarlet lump scarring my otherwise youthful face. After analyzing this monstrosity, I have come to the conclusion that it is just a pimple. A big one. The results of today’s physical exam indicate that my body and mind have reverted to those of a teenager. I feel like Symin looks at me differently. Which irritates me. I got angry when he insisted on running my blood test for me. I mean, really! What even! I can do it all by myself! …In any case, I wonder what experiment I should focus on next. The blue flame in the furnace outside is growing weaker by the day. I do hope the Guidance Stone doesn’t stop working…"
"Anti-Aging Experimental Trial Day 6
My age reversal has progressed further still. I now look and feel like a 6-year-old. My height has regressed so much that I can no longer reach things in high places. It’s super annoying. Where is that genius swordsman we placed in the Slumber of Restoration, anyway? Wake up, already! If he doesn’t awaken soon, my feature expansions for the Sheikah Sensor will go to waste. But even if he does manage to wake up, how can I be sure he’ll find me here? I want to go and just kick Linky awake, but I doubt Symin would help me. It’d be hard with my 6-year-old body anyway. Instead, I think I’ll begin working on a rune to un-reverse my aging process."
"Anti-Aging Experimental Trial Day 7
This morning's exam results indicated that I am still age 6, same as yesterday. Perhaps my age-reversal has stopped. As luck would have it, today I also finished developing the beta version of an age-boosting rune! ♪ If successful, this should be able to reverse the effects of the anti-aging rune. I hope it will, anyway. All I need to do is increase the output and expose myself to its rays… However, when I tried to add this feature to the Sheikah Slate I made, I found that the Guidance Stone had stopped! What's more, the blue flame in the furnace outside has gone out! I sent Symin to the ancient furnace, but he was too clumsy and it was raining and nothing went to plan. So I had to go down there to help, but a girl in the village saw me. What a mess I've made… Not only am I unable to continue my research in this state, I can only work by the light of gas lamps. What to do…"