The Demon Sword Master of Excalibur Academy.
Sensing that his end is near, the Undead King, one of the Dark Lords trying to take over the world, uses a reincarnation spell to return 1,000 years later. He awakens to a world at war with mysterious creatures called The Void.
I read volume 1 and I'm halfway through volume 2. I'm not sold on this one.
The main sticking point for me is that the protagonist has been reborn as a 10 year old human boy (instead of his previous immortal Undead King self) and has his human emotions reawakened.
So one minute he's reflecting on how he single-handedly destroyed armies mercilessly in his past life, the next he's getting bashful because a girl got too close.
It also seems like they're building him up to be a faux villain who was just misunderstood or whatever in his past life. He wants to rule (both in his past and present life), but his goals beyond that are kinda vague. I guess I'll stick with it a bit longer and see how it goes.
Oh God, that's one of those I should add to my LN pet peeves post. But I guess that falls under the "passive main characters" category as well. If LN characters are written as a self-insert how socially inept have the Japanese target audience have to be...