It seems pretty obvious from the opening sequence that this wasn't just some passing of the baton. Also,
the ending to the last series suggested (to me, at least) that Kouga died in the Promised Land. If that's the case, then Zaruba may have been recovered, but we could assume the armour was destroyed and had to be reforged (hence the opening).
Some other questions arise from the armour's reaction. Is it rejecting him because there's no contract? Is it trying to show him that only those with pure intent (deep down, at least) can use it? Considering these Horrors have makai energy, it could just be a reaction similar to putting two magnets together... But it could also have a much deeper meaning. Sure, he was given the Garo armour, but has he
earned it? The armour seemed to begin fully glowing only after he showed determination in cutting down the Horror. Before that, the glow seemed to be caused by an explosive release of makai energy (note the glow when he was fighting by the escalators before summoning the armour) and at first seemed to be reflected on the armour, but later the whole thing was glowing, which leads to another theory:
Could it be the Garo armour is somehow low on power and is absorbing the makai energy from the Horror to "fill its batteries"?
Gai and Lian are obviously the eye candy for this season, and I love the fact that there's now a prominent archer (too many Makai swordsmen in this world). Lian's strangely overdressed for a Makai Priest, but the outfit really seems to suit her personality thus far. She's no Rekka, but I've certainly got no complaints. I wonder if the gun was one of the new developments to make priests less of a support role after the events of last season...
I also have to wonder if the new form of Horror is also related to last season's events. Leo did a lot of experimentation with Inga when developing his technology, and this would be a viable development of that research. It also might mean the Horrors have some immunity/resistance to attack and (as Zaruba pointed out) can keep off the radar.