Been wanting to reread some manga I've read in the past.

First manga, mc is in tokyo for a school trip and visits a museum. He was looking at an exhibit and got transported to feudal japan. I think he can teleport between feudal japan and modern day japan but he goes blind in one eye.

Second manga, mc is a new teacher at an all girls school. He goes to meet his students but they turn out to be really good at using firearms and have them hidden all over their bodies. I think they also work as mercenaries.

Third manga, mc is a regular school boy until he meets a birdman who tells him he is actually the high priest of a country and that current one is an imposter who is supported by a dragon man. The dragon man sends over his subordinates over to try to assassinate the mc which include a tiger man and monkey man. They join his side after they realize he's the real high priest.

Fourth manga, mc has just died and is in the underworld. He is going to get his memory erased and be reborn but he falls in love with the the spirit/goddess that is attending to him and decides to stay in the underworld and work for them.

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I'm literally a rock.

First one sounds like Amatsuki.

For #2: There are a couple details off, but it sounds a lot like Mission! School.

#4: Might be Jigokuren - Love in the Hell. It also has a sequel, Jigokuren - Death Life.

#3 is Genjuu no Seiza