Fortunately, Tadashi is able to to convince his difficult little brother to pursue a more productive path and using his genius for good by joining him at college. The science department of this college requires revolutionary, life-changing inventions of its students.
One such invention is Tadashi's health care robot, Baymax.
Unfortunately, Tadashi meets an untimely demise, and Hiro slips into a deep depression.
Baymax in his own objective, unsubtle way is able to continue Tadashi's work in keeping Hiro off a destructive path. Hiro's develops the need to avenge his brother while Baymax's only goal is to keep Hiro safe and healthy.
Neither one expect this path would lead to a team of super heros, but there you go.
Throughout the film, Hiro meets a series of challenges that test his character, especially when faced with the opportunity to seek revenge against the man responsible for Tadashi's death. With Baymax's guidance he might have failed.
Baymax serves as a guardian angel, and he continues Tadashi's work in providing correct guidance to Hiro. Baymax keeps Hiro happy, productive, peaceful, and safe. Ultimately, he follows in Tadashi's footsteps in self-sacrifice for the good of others. By then, Hiro no longer needs guidance. He takes control of his own life and follows his brother's footsteps in the goal to invent and keep people safe.
Big Hero 6 is a incredible story with both hilarious and heart-breaking moments.
Most importantly, it leaves a haunting question: If I died today, what influence, what impression, what legacy, would I leave behind?
God made us all with a purpose and limited time to fulfill it.
Tadashi had two purposes: inventing Baymax and guiding his brother down a moral path. He is productive enough to fulfill them before his time comes to an end.