Bella and Jisoo have a very wholesome relationship, they aren't the closest out of the BlackPink members but they have a very special bond. When Bella joined YG in 2012 she was one of the youngest trainees so it was the unofficial job of the older trainees to watch over her.
Jisoo was one of the trainees that really stepped up to this job. She would help Bella with Korean, make sure she was eating, and ensure that Bella didn't overwork herself.
After the first few months of her training Bella was placed into the group of Lisa, Rosé, Jennie, and coincidentally Jisoo. After being placed in the same group Jisoo fully took on the motherly role for Bella.
As they came closer to their debut and Bella got older she became much more independent when it came to taking care of herself. Even so Jisoo continues to behave as a motherly figure to Bella.
After debut her attention turned to making sure Bella is always protected and comfortable. She can often be seen in fancams and other videos fixing Bella's clothes and covering her from cameras. She also makes sure to walk close to Bella when they are in public.
While a lot of Jisoo's actions towards Bella as trainees are unknown by fans, Bella has told stories on lives of Jisoo taking care of her. Blinks tend to miss a lot of the smaller moments between the two, but a few big moments have gained the attention of the fandom.
In 2018, BlackPink was doing a performance of D4 and Forever Young for a music festival. Bella was wearing a pink, spaghetti strap, bow top and a pair of black and white shorts with a lace up detail on the side. While performing the dance break of D4, the laces on the right side of Bellas shorts came untied and the side of her shorts began to open up. Jisoo noticed immediately from where she was and kept watching to make sure it didn't get any worse.
As they got close for the ending pose Jisoo positioned herself slightly in front of Bella to block the camera from showing her shorts and held the sides of Bellas shorts together. She then started to retie the laces making sure that they were knotted and not coming loose. She then quickly said something to Bella which she later told fans was something along the lines of "If it happens again come over to me".
Fans took notice of the moment between the two and it became a big deal for the fandom. Many fans saw it as a testament to the stories of Jisoo being a motherly figure towards Bella. The incident earned Jisoo the nickname Mother Jisoo which, to the delight of the fans, Bella saw and started using as well.
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Hey kiddos I hope you all like this chapter a little Bella x Jisoo content we love to see it anyway thanks for waiting for a chapter I am really horrible at updating. Also this is the outfit I was trying to describe lol