MÄR, Kiba Recommendations
They have very similar storylines. They are both about different worlds in a war, both have a lot of adventure. Make new friends and more. I think they both are great anime.
Kiba is a grown up version of MAR Heaven and the concepts are virtually the same. A guy (Ginta/Kiba) wants to get away from their own boring world and they manage to get sucked into another one, where they find out they're super powerful because they have ARMs/shards. Kiba's definitely targeted at an older audience though.
Both anime are about the main characters going to an alternate world. They both obtained the ability/power/weapon to fight - in MAR using ARMS and in Kiba using shards. Of course, both main leads became stronger as the anime progresses on.
However, in contrast with Kiba, MAR is a far lighter anime and with a more exciting, complex and smoother plot. Still, when i first watched Kiba, the first anime it reminded me of is MAR.