To be honest, I wouldn't.
There are some superficial similarities like having a stamina-based combat system and being able to grab your loot and xp back from the point where you died but really that's about it.
Souls games are methodically paced, atmospheric, and basically about getting to the end of the story. Nioh is way faster-paced, and less about story and atmosphere. It just gives you a fantasy version of Sengoku era Japan (there's no shortage of flavour and lore) and a load of discrete levels of ascending difficulty. Its like an old-school arcade adventure where the appeal is all about the combat and character/gear progression.
To play, its way faster than any Souls game (inc. Bloodborne) and gives you far more tools and techniques to experiment with. Its also much more technical because you have things like stances, ki-pulsing (instant stamina regen), anima and amrita resources to think about. It can come across as overwhelming at first, but you can pick and choose which aspects to focus on, and which to ignore.
The main thing is that Its all very well balanced allowing every weapon type and play style to be viable even at the hardest difficulties. Difficulty is comparable to the tougher Souls games although its way more flexible in terms of tuning the level of challenge. Its NG+ systems are way, way more fleshed out than anything From offers, to my mind playing it through once is basically scratching the surface. Its designed for replay value.
The big difference though is that Nioh is very heavy on looting and crafting, Diablo-style. They give you a base inventory of 600 slots and a further 5000 for storage and as I mentioned its really easy to find yourself jammed up if you hoard. If this is a turn-off for you, you might find it a deal-breaker. It does exist for a reason though, because gear and build is hugely important, way more than Souls'. You can also respec quite freely and the game allows you to switch up your base stats and your skill trees independently, so you don't need to worry about committing to a particular setup only to find it unfun or lacking in effectiveness.