In Ghostwire: Tokyo, you’ll need to absorb souls using Katashiro and trade these souls in for experience and money. However, you only have so many Katashiro, so you’ll need to get more to hold more souls. Our Ghostwire: Tokyo guide explains where to get more Katashiro to carry more souls.
After you clear out your first shrine, you’ll get a handful of Katashiro, but they’ll fill up fast. You can empty them out at a telephone booth, but if you want to expand your soul storage capacity, you can head to any store on the map. From there, you can buy more Katashiro from the cat shopkeepers.
The price for more can be steep, at $3,000 for one, so don’t overbuy early on. Once you get more money from side quests and the like, you can really stock up.
You don’t necessarily need more Katashiro to progress, but having more is convenient since you won’t have to stop at telephone booths as often.