Similar to Mako, the rest of Mako's friends weren't just sitting idly by but were instead training respectively to become stronger and improve their strengths.
To do so Bill and Iris had a different plan than Mako who was spending all his time utilizing the resources that the military school provided to become as strong as possible.
The strategy that Bill and Iris decided to utilize was one that wasn't theirs to begin with but rather was instructed to them by Commander Sable.
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{Day before departure to military school}
Bill was just existing inside his room still trying to cope with the tremendous loss he had suffered.
Some would say that Bill was being overly dramatic and sensitive about losing Iris after all they hadn't even been together for so long, but it is important to remember that for Bill's entire life, he had rarely ever felt the emotions of being loved and wanted.