One thing I think my L5R game has been very successful with is making NPCs that resonate with the players, and who have stories that the players want to see how they play out. Sometimes an NPC hits better than others, sure, but in general the NPCs that have showed up in the game have left a mark. This has been most true lately where NPCs have been dying around the PCs as part of the war effort against the Shadowlands. Part of this is because I have good players, but it is also partially because of how I handle the NPCs that these deaths have been felt.
NPCs Have History
The first thing I did with all the NPCs I've introduced lately is gave them a backstory. The PCs are part of the Imperial Legion and so I worked out reasons why the NPCs were in the legion as well. For some it was a family position that they were inheriting. For others they had earned their way in, or lucked into their way in, through other means. For two of the NPCs they were there to take the place of a family member who had died before discharging their service to the Legion.
This is a simple thing to do, but when you go through and actually assign a backstory to the NPCs you give it a sense of history. The Kakita girl who is in the legion because her brother died is there for very different reasons than the Shiba who, through a turn of good luck, managed to save a legion gunso in a fight a few years ago and thus earned a position. This sense of history is also important because the PCs will find echoes of themselves in some of those NPCs and that can make for a strong connection.
One of the fastest friendships I had between a PC and an NPC came about because I had one of the Scorpion NPCs come from the area of Scorpion lands that was close to Hare lands. In fact, the Scorpion's grandfather had been among those killed after the Scorpion had wiped out all of the hare save for a lone Usagi and the ronin Ujina. It gave the two characters a connection and the ability to reminisce together about home, and that made for an awesome connection.
A Plan For The Future
The other thing I did for the NPCs is I planned their future. This was done in two phases. The first is I planned what the NPC would do as things went on. Where they would end up, who they would befriend, etc. The PCs could change this through play, but I had a plan. The second phase was what the NPC wanted to do. What they planned to do with their life after the Legion, after the next battle, after the next night.
Together these give the character some depth because they have plans, goals, and a direction they're going in. They don't simply exist for the PCs or when the PCs are around, they have their own things that they are doing and plans for their future. This also means that if an NPC is off screen for a while I already know where they'll be when the PCs catch up to them again.
Both of these things have made for some more poignant deaths because the NPCs had been alive in a sense. They'd had pasts, they'd had plans for the future, they'd made friends and connections, and then they were just gone. Obviously certain NPCs falling have hurt more than others, but it's been interesting hearing after a battle how - before even concern for other PCs or their own character - a player will say that they hope Rin is still alive, or that Takechi made it through. It adds a lot of depth to the game and makes the work put in worth it, even if it means those awesome plans that I had had for the NPC are no longer able to be done, at least with that character.
Definitely something worth trying out, and something I intend to keep doing as time goes on.