Blood Magick, as far as Harry was aware, was neither all Dark Arts nor all illegal. He knew because, after finding out that it was blood wards which had forced him to live with the Dursleys, he'd done extensive research on the subject. In fact, through owl-purchase, he already owned two of the books on blood magick that were in the attic. Blood wards were completely legal unless they a) used the blood of an unwilling subject or b) used so much blood as to cause a being, be they human or creature, undue harm, stress, danger or death. Finally, blood magick was held to the same standards (legal unless it met a or b), but also held to another standard, illegal if c) the magick performed caused undue harm, influence, suffering or pain [to anyone] with an addendum against necromancy added in the late 1700s.
Harry had used blood wards on several of his possessions, including his school-trunk and the two trunks he'd taken from the attic. He'd also used blood wards on the journals he kept. These journals detailed his life, but many detailed his studies on potions, dark arts, defense against the dark arts, rites and rituals and pureblood customs and traditions. He'd begun keeping the ones attributed to his studies in his second year, but the ones detailing his life went back to the summer he'd found out he was a wizard.
By his second week at Grimmauld Place, which was also the second week of July, it became clear to Harry that Sirius was somewhat childish and also not 100% trustworthy. He liked Sirius, he enjoyed the time they spent together, he was thrilled to never have to go back to the Dursleys, or their home, and he was very happy with the connection Sirius (and Remus) gave him to his parents.
However, Sirius had definite beliefs and attitudes that Harry just could not understand. Sirius's pro-muggle, pro-equality beliefs about muggles - though he'd never spent any time with them - made no sense to Harry, who had grown up in the muggle world. Although he believed muggles were valuable and worthy of respect, he also understood the differences between the muggle and magical world. To Harry, it was simple fact that, in some very key ways, wizards were superior to muggles -- because wizards had magick. Harry never, ever, wanted to go back to a world in which he remained ignorant of magick and all it had to offer.
Sirius also had a set-in-stone belief that there were good people, there were bad people, and there were Death Eaters. To Sirius, Death Eaters were a distinct breed of human witch or wizard that were absolutely unredeemable and could never be believed or trusted no matter what -- once a Death Eater, always a Death Eater. Although Harry's life was forever changed, and miserably so in some cases, by Lord Voldemort....Harry just could not believe anything in the world was so black and white.
By the third week in July, Harry was made aware of another opinion that Sirius carried that Harry couldn't understand. Sirius felt a complete and encompassing disdain for any of the old traditions. According to Sirius, nothing he'd grown up with and nothing he'd learned from the Pureblood world of wizards, from the Black Family, or from any experience with the Old Religion was valuable or worth holding onto. Harry loved the Rites and Rituals course at Hogwarts. He loved learning the ways and rituals (circles, rites, spells, tools) of the Old Religion, and he looked forward to the Yule circle during the Christmas holidays that he'd get to participate in this year. He could not, no matter how hard he tried, figure out why Sirius was so set against anything that had come before.
The final nail in the coffin, so to speak, was Sirius's complete lack of regard for anyone else's, but especially Harry's, privacy. At least a dozen times since Harry had arrived, Sirius had barged into his room without knocking (twice by unlocking Harry's locking charms) to discuss Quidditch, or talk about Harry's dad, or tell Harry something Sirius was determined he know. Harry had repeatedly asked Sirius to knock and to respect his privacy, but the requests had been either ignored or just denied. This, coupled with Sirius's adolescent penchant for playing 'harmless' tricks on both Harry and Remus or telling off-colour jokes, made Sirius (to Harry's mind) almost completely untrustworthy.
His summer homework was complete, though there were two assignments he'd had to write to Professor Zabini about given Sirius's attitude about ritual magick; Harry had been forbidden to practice any. Although Harry wasn't abiding by that rule in the privacy of his own room, the homework required that Harry practice outside and, for one of the assignments, in the company of at least one witness.
The most unnerving thing, and the thing that put Harry the most ill-at-ease, happened exactly one-week before his birthday, while Harry had been down in the basement -- working on potions the whole of the morning.
During his third year, he'd remade all the potions from his first year, with accompanying essays -- a deal he'd worked out with Professor Snape that had earned him extra points and a bump in grade, and which Harry had every intention of doing again. So, this summer, he'd worked on nearly all of the potions from his second year, with accompanying essays. He only had a handful of potions left, and he was determined to finish them so that he could spend the school year remaking the potions from third year, and doing better over-all in potions class (and, honestly, doing better in all his classes would be ideal).
After finishing his potion, he'd left the basement and gone up to his room to shower and change. Upon entering, he'd looked around with both suspicion and paranoia. He was prone to both, having lived in a dorm full of Gryffindor boys and having lived with his Aunt Petunia. So, maybe it was a little odd that he'd left tells for himself, but that didn't change the fact that his room had been rifled through.
The piece of sellotape he'd put on his closet door was broken, a corner of the large, square rug he'd picked out and carefully placed down was turned up, two of his schoolbooks were facing the wrong way on his desk, and one of the two paintings on his walls was slightly crooked. Instead of jumping to elaborate conclusions, Harry took a deep breath.
"Kreacher?" he called quietly.
"Master Harry is needing Kreacher for something?" Kreacher asked after he popped in.
Harry shook his head. "Have you cleaned my room while I was down in the basement?" he asked.
"No, Master Harry. Kreacher has not been in Master's room. It is Friday, Master Harry. Kreacher only cleans Master Harry's bedroom on Sundays," Kreacher replied.
Harry nodded. "Can you keep my secrets, Kreacher?"
"Kreacher would be honoured to keep Master Harry's secrets! Kreacher can do this! Master Harry is the rightful heir of the noble house of Black, Kreacher heard Master Sirius say so!" Kreacher exclaimed.
"Someone has been through my things," Harry replied softly. "Someone has rifled through my room, looking through my things."
"Is this the secret Master Harry wants Kreacher to keep?" Kreacher asked.
"The first part of the secret, yes. The second part is that I am aware someone has been through my room. The third part is that I intend to rectify the situation by the use of blood wards. The fourth part is that they were probably not able to find whatever they were after because I used blood wards on that which I keep most important. Does that make sense, Kreacher?" Harry explained.
"Oh, yes, Master Harry! Kreacher understands! Kreacher will keep any and all of Master Harry's secrets!" Kreacher replied.
Harry checked under his bed, using his wand and a quick spell to detect the trunk that had been hidden by House-Elf magick underneath the bed. "It is a very good thing that I had you hide this trunk, but an even better decision to spell them both to look like extra school-trunks and that they are both warded by blood magick. Thank you, Kreacher, for your help in this matter. I trust you to keep your silence. You may go," he said.
Kreacher bowed and then popped away.
Harry stood, then straightened his room. Though he regretted the necessity for it, he'd work on the blood wards to lock the door to his room tonight. They wouldn't need to be overly complex, a simple blood ward would do to keep Sirius, and anyone else, out. Although he was blood-keyed to the Black estate, having been made heir, his blood was entirely Potter-blood, and therefore could not be overcome by the link he shared with Sirius through the heir-naming ceremony he'd gone through at the very end of June.
Later that night, after performing the blood-magick on his room, Harry drafted a letter to Gringotts. It was time he knew exactly where he stood, financially and with the Potter properties and anything else he had inherited.
He knew his largely-undeserved fame had probably wrought some degree of gifts, fanfare and funds, but before now it had never occurred to him to inquire about it. If the Gringotts goblins didn't know, then he'd take up the matter with a solicitor to see what he had and where it was.
Harry had avoided Sirius and Remus all day, shucking the routine he'd gotten into for the safety of his room -- made much safer now by the blood wards.
His favored routine had made him feel more like an adult than a nearly-fourteen year-old boy, but that couldn't really be helped. He'd never had much of a childhood, being made to slave away for the Dursleys, and although living with Sirius was better, Sirius often confused him with James. As such, it was clear to Harry that Sirius treated him much like he might another adult instead of a kid who needed chores, structure, rules and consequences for breaking them.
Harry rose every morning, changed into muggle work-out attire and walked down, and across, the hall to the little muggle-gym that Sirius had set up for Remus. Working out helped Remus with some of the wolf-behaviour, and Harry was grateful for it. He did a fifteen-minute run on the treadmill every morning followed by fifteen minutes of sit-ups and pull-ups, followed by fifteen minutes of yoga. Since all the exercise he'd ever really known before was running away from Dudley and his gang or manual labor or Quidditch, Harry was grateful for the chance (with well-rounded meals and an exercise regime) to get in better, healthier shape.
He wanted to be better equipped for what may lie ahead in his future -- he no longer believed that he'd have any sort of chance at a normal life. Lord Voldemort would, somehow, return and there would be a war. Harry was certain of it.
After working out, he would shower, dress, have a light breakfast and then do some reading. Sometimes he read in the Black Family Library, other times in his room. He took notes, and in some cases he'd do a bit of homework after. He'd tidy his room, then call for Kreacher to discuss anything that needed to be done or gotten that day. By this time both Sirius and Remus would typically be awake and he would join them for a cup of tea, or two, while they breakfasted.
Once he was done with that bit of socializing, Harry would take on some chore or other. Lately, he'd been in the back garden weeding, pruning, planting, watering and harvesting the garden. While it wasn't extensive, it did have several herbs and potions ingredients that Harry couldn't bear to see go to waste. What he couldn't use, they sold or gave away.
Generally, after a chore or two, Harry would sit in the second of the two parlours on the ground floor and respond to his mail. Because post-Owls couldn't reach Grimmauld Place, the House-Elf Harry hadn't yet met (who did all the cooking and cleaning) was charged with going to the post-Office in Diagon Alley every single day and bringing back all the mail and any packages for the group. Harry's mail always sat on the side-table near the purple armchair (the armchair that he preferred), if he had any. When he was finished, he'd give the sealed correspondence to Kreacher who would deliver it. Hedwig had been very unhappy about the arrangement, so he'd sent her to live with Hermione for the summer -- whom he knew would benefit from the use of his owl.
Afterwards, Harry would take lunch in either the solarium or his room, then he'd retire to his room for a bit of a nap. After the nap, he'd hunt up Remus and they'd do some course review. Sometimes the review would take place in the Duelling Chamber, which was on the first floor, other times it would be entirely book-review in the library. Then all three of them would have tea in the first parlour -- often times they were joined for tea by Professor Dumbledore or Auror Nymphadora Tonks who, as it happened, was Sirius's cousin. Twice both Tonks, as she liked to be called, and her mother, Andromeda, had joined them for tea. Harry found that he liked it best when someone else showed up for tea.
Once tea was over, Harry would head back to his room to do whatever he liked, or he'd spend time exploring the house -- it seemed as though there was always something to discover about Grimmauld Place. Early in the evening, he'd have dinner with Sirius and Remus -- which was usually a long affair, and was occasionally a meal where they were joined by one of the Weasley adults -- Arthur, Bill or Charlie -- or someone else of either Professor Dumbledore's or Sirius's acquaintance.
It was between when this meal was over and bedtime that Harry would find himself a bit bored. He couldn't go to bed too early, or he'd be awake at a dreadfully early hour, but after dinner there felt as though there were too many hours with very little, if anything, to occupy his time and energy. He missed Ron and Hermione. He lacked the company of someone his own age, and it was starting to get to him.
And so, in that fashion, his summer had begun to pass by, but...Harry could feel that a fight or argument would be coming soon. There was no way he'd get away with using blood wards for his room without Sirius noticing and wanting to 'have a talk' about it. And, Harry imagined, he'd never get away from Sirius before they began, yet again, a dreary discussion about the dangers of the Dark Arts.