Anyone know what this anime is called?

I saw a couple episodes of this in the Panda Hotel in Hong Kong. It's Cantonese dub and it was on along with Kamichama Karin and Prince of Tennis. I only remember that there were two main characters and one wore red and the other wore blue. They had pet monsters that, when not fighting, were kept in . When they were needed again, they would shoot them out of things equipped to their arms. I don't remember a lot, but I've been searching for this anime for ages! It would really be a big help if you were to know. Thanks vey much!!