Grandparents

Akane's parents were really close to Rin, Raiden and Shizuka when they were children.

Hisao was a seasoned adventurer in his youth and made a reputation for being tougher than the toughies and smarter than the smarties (see what I did there, Woo-Ooo!), while Noriko was perhaps the greatest ninja of her generation, with a finesse in technique never seen before and a huge amount of skill. The two got married while they were young and had 4 kids.
After Akane disappeared, Hisao and Noriko took part in taking care of Rin and Raiden (alongside Jun). It is said that part of Raiden's personality comes from his grandfather, while Rin got the kindness of her grandmother.

Sorry for the feels...It just happened something with a dear family member during the weekend and I'm really worried about him...