How does Kakashi have the Mangekyou Sharingan?

[Allan Hoshigaki]

I think you get MS from realizing and accepting a loss of a loved one.

Itachi did not kill Shiusi but has MS
Sasuke did not kill Itachi but has MS

So Kakashi probably accepted that Obito's death wasn't his fault and accepted it

itachi killed shisui he fully admitted to that.

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itachi said he helped shisui dispose of his body which means he help kill shisui even though shisui told him too. itachi still killed him. they both didnt goto the meeting. and itachi killed him with shisui permission and itachi disposed of his body keeping his MS. also shisui did write that note that they found

 

[senjumahe]

may b rin died just few years ago.

 

[Lentz]

I want to see Yamamoto's bankai.

 

[Uchiha Gohan]

He unlocked the MS due to the fact of using the search bar.