MTL - Strange Worlds: The Sequence - Chapter 43 Oniichi

Our protagonist was a Mexican who died on a flight, when he woke up he found Apollo who reincarnated him as the grandson of Gaius Octavian Turino (Augustus) the first Roman emperor, having a mission in hand to conquer the New World to save the Roman polytheist world and his existence.

Fate, a gatekeeper who had been working for the castle, is beset by a few burdens.

Failing in his job hunting, Sanada Kyouichirou was hopeless in this society. When kyouichirou had thrown himself towards the bottom of a cliff. When he woke up his body had returned towards when he was in fifth grade of elementary school. He did not want to have any regrets in this life so he had decided on building up an harem in this second life.

The elder sister that he admired, a senior and president of the student council at a school for rich young girls, a strong minded upper classman at school. The poison fang of Kyouichirou who had pretended to be a innocent child attacks those girls.