[TOMT] Older anime about time traveling/parallel timelines
I watched this anime sometime between early 2000s to \~2015, most definitely leaning to the late 2000's early 2010s.
The main character lived with his sister (probably no parents?) and they had this old round rock artifact that their parents left behind, probably archaeologists?
One day another girl character becomes aggressive towards the sister, I forget most of the middle of the anime, but the ending reveals that the artifact was a timeline/parallel dimension tool and he's able to reverse his parents' deaths and have his sister, except in this timeline she's a baby
Main points I do remember:
\- round rock-like ancient artifact
\- sister becomes baby at the end, they were closer in age before
\- definitely not anything newer, highly doubt it's after 2014
\- modern day setting, no big scifi fantasy setting