Rex Striker is hard at work, but he isn't training or fighting with anyone, he's just reading some of the many books that occupy the Infinite Library. Why is he doing this? Because Wyse and Tome told him to.
Tome: Due to the nature of your abilities, we've decided, upon much deliberation, that the best way to train you is to help you train yourself. Let me explain, you specialize in a skill called Soul Entity Creation, you seem to think of your constructs as just weapons, but they can be so much more than that. (Tome explains to him)
Wyse: Soul entities have a mind of their own, they have thoughts, emotions, and sometimes even feelings, and it's all derived from their creator. Their intelligence may vary, but their capacity for knowledge is there, and you need to work on that. (Wyse tells him)