Actually, after doing some hard thinks, I may have found the deciding factor that pushes this to Otus' favor. Combat experience.
See, Ika is not a very combat oriented character, and I'm pretty sure that most of her combatfeats are simply instinctual fighting habits, so while there's no doubt that she can fight, Otus has fought against a lot more impressive characters, on top of his formal training under the much wiser Owl, Asio. Heck, many of his fights could have prepared him for this one, such as when he fought the Guardian to the Hex Machine, a blob-like monster that, among its various attacks, uses its giant blobby arm to try to either smack or strike at Otus. It's weak point in the first part of the boss battle is even the module located on its head. (Before Otus made it electrocute itself.) And when fighting Dirk, he had to dodge many, many incoming knives that he threw at Otus, so that would help with dodging the tentacles.
So, unless there are some really good fights that I'm unaware of that Ika has done, this is basically the case of Otus using all of the skills he's accumulated to this point to fight, while Ika doesn't really know how to deal with Otus except try to use her tentacles on him a lot. This is close, really close, but I feel that, more often than not, Otus' variability, agility, and combat experience will allow him to win more often than not.
Winner: Otus
