I don't own Harry Potter or related works only the OC

From the African continent it wasn't hard to find a boat that would go to the US, thought the journey was painfully boring. 

After reaching the US while the muggle paperwork lasted about an hour, the magical paperwork took literal days to even start being processed not to mention the fact that since I had all kind of magical tattoos on my body they forced me to strip completely naked so that they could observe and make sure none of those symbols were dark. They treated me like I was some kind of bloody animal. Fortunately they never thought about checking my soul, seeing as soul magic is forbidden and an absurdly dangerous art with signs that are usually pretty obvious like insanity.

After all the different checkups and paying a lot of people in order to forget my none human origin, I was finally allowed to enter the damn country. 

It took me travelling across the damn continent for nearly a year to finally find someone who could lead me to a native American magical, though I did lose a large portion of my giant inheritance over the year, but it was still worth the trouble.

Originally no native American magical wanted to teach me their magic but, after seeing my tattoos, they were willing to lead me to someone who might have been willing to teach me their magic.

The Native American magical community turned out to be spread across all the nature preserves from the continent. Way better than the British bar leaky cauldron.

Of course that was the native American magical community, not the American wizarding community. 

Fortunately, for me it wasn't that uncommon for wizards to try and learn native American magic, but they usually give up after realising how much more complex their magic is while there is also the fact that native American magical use spirits or animals to use their magic which all wizards write off as dark magic. 

The only reason I had it so hard was because thanks to my half giant ancestory, a lot of people didn't trust me or l looked down by others.

Timeskip 5 years 

After 5 years of studying under them did I get to finally learn the spell that I was trying to learn. The spell was something that was considered a useless spell in the eyes of most wizards.

The spell allowed a person to permanently get the property of one non magical creature, but not only could it only be used once, the property was usually a degraded version of that non magical creature. The spell also needed years of study to master and you could only use it once.

Now wizards might not really see the point of learning such a spell, but for someone who remembers spending hours on youtube looking at interesting fact video, I could say that I saw the true potential of the spell.

After making sure I had fully understood the spell and could properly use it, I went to the nearest university with a good biology department and made liberal use of memory charm to borrow some of their equipment, of course I tried to see if they know the creature I was looking for, but they didn't.

The next few months I ended up travelling from one body of water to another. Nearly a year later I found what I was looking for the hydra. (A/N: for those who don't know look up immortal animals.)

 After that all I had to do was use the spell while concentrating on the regenerative property of the hydra.

I could literally feel the magic changing me, my giant blood fusing with the degraded version of the hydra's regenerative property to literally make me unageing.

After that I did have to do a lot of tests to discover how it affected me. It turned out that while I expected my new regenerative property to only stop me from ageing, it actually also allowed me to regenerate entire limbs given that I have enough energy and food to support the regeneration. Fortunately it seems like my severed limbs to not regenerate whole new bodies, yeah I didn't think I was ready for clones of myself.

After many years I was able to do what I had set out to do, attaining immortality. After all what were the chances of being reborn in a better world than this.

Now after many years I stopped fusing magic into my body, and just brought it under my control, after all I didn't want to increase my bodies magic immunity to the point it undoes my Immortality.

Now that I had a really strong unageing body that was immune to killing curse, I went to Switzerland to my dwarves bank, where I paid most of my inheritance to build me a weapon and armour. 

After that I truly started my new life as a hit wizard and a semi-vigilante, since I did take money from the criminal organisations while also killing those that the world was better without.