First thanks for the super helpful summary -- trying to keep everything staright is getting increasingly difficult with this series.
Second, I think the Mangaka intentionally made Shinoda and Hina look alike. It feeds into the inevitable conspiracy Iijima is starting to weave -- that he was Shinoda's replacement because of their shared name, and Hina is the new replacement for Shinoda probably because of their looks or personality or both. Or at least that is how I expect Iijima to weave his lies in the next chapter -- "Chi doesn't actually love you, he loves Shinoda and you have his face". I suspect Iijima had either started to develop feelings for Chi, or was jealous that Chi was getting the happy ending he couldn't have and reacted like that (or a mix of both, though I lean towards jealousy).
For those who were confused (as I am) I re-read and I hope this will help:
1. Iijima Hisashi was/ is in love with Shige-san (Chii Masato’s friend/ senpai).
2. Shige-san knew about the two Hisashi and he is a 120% hetero and cannot accept the feelings of Iijima Hisashi… so in a way, he push Chii (for he wants Chii to forget the Shinoda Hisashi) and Iijima Hisashi. He felt guilty and at the same time he felt that it was his fault… For thinking that maybe Iijima Hisashi and Masato may fall in love and forget about their ‘unrequited love’ : “If Masato’s loneliness will be eased… If it becomes the trigger to Iijima Hisashi breaking off his obsession with me…”
BUT - from his own words: “I wanted to give him a place to run and called Masato over to Tokyo once he graduated… Masato, who I had prepared to look after for the rest of my life and brought out of our hometown let alone protecting him…”
Shige-san loves Masato in a way a father or a brother loves his son or his little brother.
3. Chii-san confess to Shinoda Hisashi when Shinoda Hisashi visited him in Tokyo - Iijima Hisashi found out about it and Chii-san told Iijima Hisashi that Shinoda Hisashi will think about it… that Shinoda Hisashi doesn’t want Chii out of his life… Iijima Hisashi “RUINS” everything when he gave Shinoda Hisashi photos of the ‘lewd’ Chii-san…
4. Shige-san explains everything to Hinase Michi (Hina)… and that Fune - the black haired guy - is special… special because “There was a time that he was taken care of in many ways by Masato, so he’s attached to him. He’s sensitive to that guy’s change.”
What I don’t really get was - why did Sensei (the mangaka/ author) drew Shinoda Hisashi and Hinase Michi (Hina) with the same MOLE on their lower left eye… It makes me confused and at the same time, felt that Chii is still in love with Shinoda…
Oh well… a few more chapters to learn the truth… worth the wait.