Did he know he was going to leave? I find it hard to believe that he didn't. That something so troubling happened in the spam of 12 hours that he was unable to return to Makochi until 3 days later just to say good bye.

That what if he got too comfortable? He was enjoying his routine over the course of summer break. He let down his guard and began to see himself as Suo, not Sun Fei. That maybe his master noticed the same thing and made him step up and take on more responsibilities.

Those in his town are also surprised to see him around more. He's there now day and night. He hadn't been there like that since before middle school.

He needed to be reminded that he is an officer of the Red Chanpuru, not a Vice Captain of Class 1-1 for Bofurin. He was to be much more than someone to pull another person to the top. Perhaps his master would make sure that Sun Fei would never forget that.

mark if the headcanon is right or wrong

✔ Nancy is very good at walking in platform heels.

She  prefers  a  mid  to  short  heel  but  she  can  walk  in  any type of heel just  fine.  It  took  some  practicing  in  her  bedroom  to  master  it.  Nancy  puts  a  lot  of  thought  and  effort  into  her  outfits  because  she  wants  to  feel  pretty  and  feminine  in  them.  Platform  heels  don't  tend  to  work  with  her  style,  they're  a  bit  too  high.

✔ Nancy likes board games, but no one else wants to play with them.

Nancy  can  get  extremely  competitive.  Unfortunately,  because  she's  so  annoying  about  it,  nobody  plays  Monopoly  with  her after  that one time she  took  it  way too  seriously. She got  into  an  argument  about  how  many  loans  were  requested  from  the  bank  which  she  considered  cheating.  Nancy  has  joined  one of  Mike's  D&D  campaigns, even  going  so  far  as  to  dress  up  as  her  character,  when  she  was  younger  and  it  wasn't  seen  as  lame  to  hang  out  with  your  baby  brother  but  she  hasn't  played  in  a  long  time. If she let herself, she'd probably enjoy it quite a lot.

✖ Nancy can't sit in a chair properly.

Her  parents  drilled  into  her  the  importance  of  good  manners  like  sitting  up  straight,  no  elbows  on  the  table  at  dinner,  no  bad  language,  all  that  bullshit  that  doesn't  matter  as  much  as  showing love and support to  your  eldest child.  For  the  most  part,  Nancy  does  uphold those good  manners and has control over her posture.  If  she's  feeling  particularly  on  edge,  she  struggles  to  sit  still. Sitting still feels like inaction when she could be doing something productive.  She'll  lean  forward, cross  her  arms  or  stand  up  and  pace. Not quite as much as Mike does.

✔ Nancy has chronic nightmares.

Nancy's  nightmares  started  after  finding  out  that  Barbara  was  dead.  She  hears  her  screams  and  sees  the  demogorgon  hunting  her, unable  to  get  to  her  in  time.  They  weren't  chronic  until  after  Vecna's  vision  and  invasion  of  her  mind.  Since  then,  the  nightmares  became  more  distressing and felt real.  It will take her a moment to determine reality when she wakes up. She usually puts on a dim light to try to sleep, she can't relax in total darkness. When  Holly  is  taken  and  her  parents  are  attacked,  her nightmares  get increasingly  violent.  Nancy  is  too  stubborn  to  take  anything  to  help  her  sleep.  Part  of  her  doesn't  want  to  sleep  because  she  knows  the  nightmares  are  waiting but  she  won't  see  anyone  about  it.  She  doesn't  trust  doctors  to  listen  to  her, especially  the ones  who  smoke  and  call  her  sweetheart.

✔ Nancy can beat you up if deserved.

She  absolutely  could  but  she  chooses  not  to.  Nancy  prefers  to  'fight back'  with  sharp  words  or  an  unimpressed  look  that  says  everything.  Physical  fights  make  her  roll  her  eyes,  especially  when  it's  guys  being  stupid, she'd rather rise above it and try to talk things through like an adult.  As  an  officer,  she  works to diffuse  any  violent  situations  as  fast  as  possible  without  escalation,  however, on rare occasions,  if she's not given much of a choice, she  does  have  to  subdue  idiots. Don't  underestimate  her  because of her size, she  can,  and  will,  kick  ass.